Allergies

1. What causes Allergies and who is at risk?
2. What are the symptoms of an Allergy?
     2.1 Allergic Rhinitis
     2.2 Asthma
     2.3 Allergic Eyes
     2.4 Allergic Eczema
     2.5 Hives
     2.6 Allergic Shock
3. How are Allergies diagnosed?
4. How are Allergies treated?
5. Drugs rating
6. Where are allergens?
7. Discussion and questions

Allergy is a hypersensitive disorder of the immune system. Allergic reactions occur to normally harmless environmental substances known as allergens; these reactions are acquired, predictable, and rapid. Strictly, allergy is one of four forms of hypersensitivity and is called type I (or immediate) hypersensitivity. It is characterized by excessive activation of certain white blood cells called mast cells and basophils by a type of antibody known as IgE, resulting in an extreme inflammatory response. Common allergic reactions include eczema, hives, hay fever, asthma attacks, food allergies, and reactions to the venom of stinging insects such as wasps and bees.

Mild allergies like hay fever are highly prevalent in the human population and cause symptoms such as allergic conjunctivitis, itchiness, and runny nose. Allergies can play a major role in conditions such as asthma. In some people, severe allergies to environmental or dietary allergens or to medication may result in life-threatening anaphylactic reactions.

A variety of tests now exist to diagnose allergic conditions; these include testing the skin for responses to known allergens or analyzing the blood for the presence and levels of allergen-specific IgE. Treatments for allergies include allergen avoidance, use of anti-histamines, steroids or other oral medications, immunotherapy to desensitize the response to allergen, and targeted therapy.

What causes Allergies and who is at risk?

An allergy is caused by an oversensitive immune system, which leads to a misdirected immune response. The immune system normally protects the body against harmful substances, such as bacteria and viruses. When an allergic reaction occurs, it is a result of the immune system reacting to substances (allergens) that are generally harmless and in most people do not cause an immune response.

Risk factors for allergy can be placed in two general categories, namely host and environmental factors. Host factors include heredity, gender, race, and age, with heredity being by far the most significant. However, there have been recent increases in the incidence of allergic disorders that cannot be explained by genetic factors alone. Four major environmental candidates are alterations in exposure to infectious diseases during early childhood, environmental pollution, allergen levels, and dietary changes.

Food allergens

One of the most common food allergies is a sensitivity to peanuts. Peanut allergies may be extremely severe, but can sometimes be outgrown by children school-age. Tree nuts, including pecans, pistachios, pine nuts, and walnuts, are another common allergen. Sufferers may be sensitive to one, or many, tree nuts. Also seeds, including sesame seeds and poppy seeds, contain oils where protein is present, which may elicit an allergic reaction.

Egg allergies affect about one in fifty children but are frequently outgrown by children when they reach age five. Typically the sensitivity is to proteins in the yolk, rather than the white.

Milk, from cows, goats or sheep, is another common allergy-causing food, and many sufferers are also unable to tolerate dairy products such as cheese. A small portion of children with a milk allergy, roughly ten percent, will have a reaction to beef. Beef contains a small amount of protein that is present in cow’s milk.

Other foods containing allergenic proteins include soy, wheat, fish, shellfish, fruits, vegetables, spices, synthetic and natural colors, and chemical additives.

Non-food protein allergens

Latex can trigger an IgE-mediated cutaneous, respiratory, and systemic reaction. The prevalence of latex allergy in the general population is believed to be less than one percent. In a hospital study, one in 800 surgical patients (0.125 percent) report latex sensitivity, although the sensitivity among health care workers is higher, between seven and ten percent. Researchers attribute this higher level to the exposure of health care workers to areas with significant airborne latex allergens, such as operating rooms, intensive care units, and dental suites. These latex-rich environments may sensitize health care workers who regularly inhale allergenic proteins.

The most prevalent response to latex is an allergic contact dermatitis, a delayed hypersensitive reaction appearing as dry, crusted lesions. This reaction usually lasts 48 to 96 hours. Sweating or rubbing the area under the glove aggravates the lesions, possibly leading to ulcerations. Anaphylactic reactions occur most often in sensitive patients, who have been exposed to the surgeon’s latex gloves during abdominal surgery, but other mucosal exposures, such as dental procedures, can also produce systemic reactions.

Latex and banana sensitivity may cross-react; furthermore, patients with latex allergy may also have sensitivities to avocado, kiwi, and chestnut. Clinically, these patients often have perioral itching and local urticaria. Only occasionally have these food-induced allergies induced systemic responses. Researchers suspect that the cross-reactivity of latex with banana, avocado, kiwi, and chestnut probably occurs because latex proteins are structurally homologous with some plant proteins.

Toxins interacting with proteins

Another non-food protein reaction, urushiol-induced contact dermatitis, originates after contact with poison ivy, eastern poison oak, western poison oak or poison sumac. Urushiol, which is not itself a protein, acts as a hapten and chemically reacts with, binds to, and changes the shape of integral membrane proteins on exposed skin cells. The immune system does not recognize the affected cells as normal parts of the body, causing a T-cell-mediated immune response. Of these poisonous plants, sumac is the most virulent. The resulting dermatological response to the reaction between urushiol and membrane proteins includes redness, swelling, papules, vesicles, blisters, and streaking.

Estimates vary on the percent of the population that will have an immune system response. Approximately 25 percent of the population will have a strong allergic response to urushiol. Generally, approximately 80 percent to 90 percent of adults will develop a rash if they are exposed to .0050 milligrams (7.7×10⁻⁵ gr) of purified urushiol but some people are so sensitive that it only takes a molecular trace on the skin to initiate an allergic reaction.

Genetic basis

Allergic diseases are strongly familial: identical twins are likely to have the same allergic diseases about 70% of the time; the same allergy occurs about 40% of the time in non-identical twins. Allergic parents are more likely to have allergic children, and their allergies are likely to be more severe than those from non-allergic parents. Some allergies, however, are not consistent along genealogies; parents who are allergic to peanuts may have children who are allergic to ragweed. It seems that the likelihood of developing allergies is inherited and related to an irregularity in the immune system, but the specific allergen is not.

The risk of allergic sensitization and the development of allergies varies with age, with young children most at risk. Several studies have shown that IgE levels are highest in childhood and fall rapidly between the ages of 10 and 30 years. The peak prevalence of hay fever is highest in children and young adults and the incidence of asthma is highest in children under 10. Overall, boys have a higher risk of developing allergy than girls, although for some diseases, namely asthma in young adults, females are more likely to be affected. Sex differences tend to decrease in adulthood. Ethnicity may play a role in some allergies; however, racial factors have been difficult to separate from environmental influences and changes due to migration. It has been suggested that different genetic loci are responsible for asthma, specifically, in people of European, Hispanic, Asian, and African origins.

Hygiene hypothesis

According to the hygiene hypothesis, proposed by David P. Strachan, allergic diseases are caused by inappropriate immunological responses to harmless antigens driven by a TH2-mediated immune response. Many bacteria and viruses elicit a TH1-mediated immune response, which down-regulates TH2 responses. The first proposed mechanism of action of the hygiene hypothesis stated that insufficient stimulation of the TH1 arm of the immune system lead to an overactive TH2 arm, which in turn led to allergic disease. In other words, individuals living in too sterile an environment are not exposed to enough pathogens to keep the immune system busy. Since our bodies evolved to deal with a certain level of such pathogens, when it is not exposed to this level, the immune system will attack harmless antigens and thus normally benign microbial objects—like pollen—will trigger an immune response.

The hygiene hypothesis was developed to explain the observation that hay fever and eczema, both allergic diseases, were less common in children from larger families, which were presumably exposed to more infectious agents through their siblings, than in children from families with only one child. The hygiene hypothesis has been extensively investigated by immunologists and epidemiologists and has become an important theoretical framework for the study of allergic disorders. It is used to explain the increase in allergic diseases that has been seen since industrialization, and the higher incidence of allergic diseases in more developed countries. The hygiene hypothesis has now expanded to include exposure to symbiotic bacteria and parasites as important modulators of immune system development, along with infectious agents.

Epidemiological data support the hygiene hypothesis. Studies have shown that various immunological and autoimmune diseases are much less common in the developing world than the industrialized world and that immigrants to the industrialized world from the developing world increasingly develop immunological disorders in relation to the length of time since arrival in the industrialized world. Longitudinal studies in the third world demonstrate an increase in immunological disorders as a country grows more affluent and, presumably, cleaner. The use of antibiotics in the first year of life has been linked to asthma and other allergic diseases. The use of antibacterial cleaning products has also been associated with higher incidence of asthma, as has birth by Caesarean section rather than vaginal birth.

Other environmental factors

International differences have been associated with the number of individuals within a population that suffer from allergy. Allergic diseases are more common in industrialized countries than in countries that are more traditional or agricultural, and there is a higher rate of allergic disease in urban populations versus rural populations, although these differences are becoming less defined.

Exposure to allergens, especially in early life, is an important risk factor for allergy. Alterations in exposure to microorganisms is another plausible explanation, at present, for the increase in atopic allergy. Endotoxin exposure reduces release of inflammatory cytokines such as TNF-α, IFNγ, interleukin-10, and interleukin-12 from white blood cells (leukocytes) that circulate in the blood. Certain microbe-sensing proteins, known as Toll-like receptors, found on the surface of cells in the body are also thought to be involved in these processes.

Gutworms and similar parasites are present in untreated drinking water in developing countries, and were present in the water of developed countries until the routine chlorination and purification of drinking water supplies. Recent research has shown that some common parasites, such as intestinal worms (e.g. hookworms), secrete chemicals into the gut wall (and hence the bloodstream) that suppress the immune system and prevent the body from attacking the parasite. This gives rise to a new slant on the hygiene hypothesis theory — that co-evolution of man and parasites has led to an immune system that only functions correctly in the presence of the parasites. Without them, the immune system becomes unbalanced and oversensitive. In particular, research suggests that allergies may coincide with the delayed establishment of gut flora in infants. However, the research to support this theory is conflicting, with some studies performed in China and Ethiopia showing an increase in allergy in people infected with intestinal worms. Clinical trials have been initiated to test the effectiveness of certain worms in treating some allergies. It may be that the term ‘parasite’ could turn out to be inappropriate, and in fact a hitherto unsuspected symbiosis is at work.

Acute response

In the early stages of allergy, a type I hypersensitivity reaction against an allergen, encountered for the first time, causes a response in a type of immune cell called a TH2 lymphocyte, which belongs to a subset of T cells that produce a cytokine called interleukin-4 (IL-4). These TH2 cells interact with other lymphocytes called B cells, whose role is production of antibodies. Coupled with signals provided by IL-4, this interaction stimulates the B cell to begin production of a large amount of a particular type of antibody known as IgE. Secreted IgE circulates in the blood and binds to an IgE-specific receptor (a kind of Fc receptor called FcεRI) on the surface of other kinds of immune cells called mast cells and basophils, which are both involved in the acute inflammatory response. The IgE-coated cells, at this stage are sensitized to the allergen.

If later exposure to the same allergen occurs, the allergen can bind to the IgE molecules held on the surface of the mast cells or basophils. Cross-linking of the IgE and Fc receptors occurs when more than one IgE-receptor complex interacts with the same allergenic molecule, and activates the sensitized cell. Activated mast cells and basophils undergo a process called degranulation, during which they release histamine and other inflammatory chemical mediators (cytokines, interleukins, leukotrienes, and prostaglandins) from their granules into the surrounding tissue causing several systemic effects, such as vasodilation, mucous secretion, nerve stimulation and smooth muscle contraction. This results in rhinorrhea, itchiness, dyspnea, and anaphylaxis. Depending on the individual, allergen, and mode of introduction, the symptoms can be system-wide (classical anaphylaxis), or localized to particular body systems; asthma is localized to the respiratory system and eczema is localized to the dermis.

Late-phase response

After the chemical mediators of the acute response subside, late phase responses can often occur. This is due to the migration of other leukocytes such as neutrophils, lymphocytes, eosinophils and macrophages to the initial site. The reaction is usually seen 2–24 hours after the original reaction. Cytokines from mast cells may also play a role in the persistence of long-term effects. Late phase responses seen in asthma are slightly different from those seen in other allergic responses, although they are still caused by release of mediators from eosinophils, and are still dependent on activity of TH2 cells.

Protein structure and organization

A protein is made from a long chain of amino acids, also known as a polypeptide chain, linked via peptide bonds. The higher order structure of a protein depends on the sequence of amino acids which form its primary sequence, as various non-covalent interactions between these amino acids ensure proper protein folding. Proteins have specific amino acid sequences, which all identical proteins share. The twenty different amino acids differ in their side chains, which are relatively large and somewhat polar. These individual amino acids are known as monomers, in the polymer chain known as the protein, which assembles through polymerization.

A protein’s secondary structure is created by hydrogen-bond interactions between the amide and carboxyl groups of the amino acid backbone. Secondary structure includes the formation of alpha helices and beta sheets. The tertiary structure is the overall shape of the protein, and is usually driven by the protein’s tendency to orient hydrophobic amino acid side chains internally, although hydrogen bonding, ionic interactions and disulfide bonds also help to stabilize proteins in the tertiary state. Quaternary structure is the overall combination of polypeptide subunits to form the functional unit. All levels of protein structure are based on the previous level. If there is an error in the primary structure of the protein this will carry to the higher levels.

Protein function

Protein folding is essential to the overall function of the individual protein. Polypeptide chains are often very long and flexible, which leads to a wide variety of ways for a protein to fold. Non-covalent interactions control the shape and structure of the nascent protein. While a single non-covalent bond is very weak, a combination of many weak bonds provide the needed strength and structure for a given protein. Electrostatic interactions, hydrophobic interactions, hydrogen bonds and van der Waals attractions all aid in protein folding. The specific polar and non-polar side chains of amino acids are also involved the protein’s folding and, in turn, its function. The final folded structure of a protein is protein’s conformation. A protein’s proper amino acid sequence is absolutely required to induce proper folding into the quaternary structure. Two common folding patterns seen in proteins are the alpha helix and beta sheets.

The function of a protein is directly determined by its structure, specifically the aforementioned non-covalent bonds. Proteins interact with other molecules at unique protein binding sites on the ligand. Proteins can have a myriad of functions, including the enzymatic catalysts which facilitate essential reactions in cells. Proteins can also act as a cell signal receptor, essential to initiating cellular responses to chemical signals, or as motor proteins, which are involved with movement of or within individual cells. Another example of protein function is that of structural proteins, which enable cell flexibility and support stability.

Proteins and the immune system

The ways in which proteins develop and fold give them their structure; some protein structures allow them to resist degradation in the acidic environment of the digestive tract. Others, which might function as cell signal receptors, can be structurally changed by the attachment of other cells. In both cases, the addition of a cell to a protein, its partial degradation, or its survival of the digestive system causes the immune system to tag the cell as foreign and dangerous. This tagging causes an allergic response.

What are the symptoms?

The parts of the body that are prone to react to allergies include the eyes, nose, lungs, skin, and stomach. Although the various allergic diseases may appear different, they all result from an exaggerated immune response to foreign substances in sensitive people. The following brief descriptions will serve as an overview of common allergic disorders.

Allergic Rhinitis

Allergic rhinitis (“hay fever”) is the most common of the allergic diseases and refers to seasonal nasal symptoms that are due to pollens. Year round or perennial allergic rhinitis is usually due to indoor allergens, such as dust mites, animal dander, or molds. It can also be caused by pollens. Symptoms result from the inflammation of the tissues that line the inside of the nose (mucus lining or membranes) after allergens are inhaled. Adjacent areas, such as the ears, sinuses, and throat can also be involved. The most common symptoms include:

• Runny nose
• Stuffy nose
• Sneezing
• Nasal itching (rubbing)
• Itchy ears and throat
• Post nasal drip (throat clearing)

In 1819, an English physician, John Bostock, first described hay fever by detailing his own seasonal nasal symptoms, which he called “summer catarrh.” The condition was called hay fever because it was thought to be caused by “new hay.”

Asthma

Asthma is a breathing problem that results from the inflammation and spasm of the lung’s air passages (bronchial tubes). The inflammation causes a narrowing of the air passages, which limits the flow of air into and out of the lungs. Asthma is most often, but not always, related to allergies. Common symptoms include:

• Shortness of breath
• Wheezing
• Coughing
• Chest tightness

Allergic Eyes

Allergic eyes (allergic conjunctivitis) is inflammation of the tissue layers (membranes) that cover the surface of the eyeball and the undersurface of the eyelid. The inflammation occurs as a result of an allergic reaction and may produce the following symptoms:

• Redness under the lids and of the eye overall
• Watery, itchy eyes
• Swelling of the membranes

Allergic Eczema

Allergic eczema (atopic dermatitis) is an allergic rash that is usually not caused by skin contact with an allergen. This condition is commonly associated with allergic rhinitis or asthma and features the following symptoms:

• Itching, redness, and or dryness of the skin
• Rash on the face, especially children
• Rash around the eyes, in the elbow creases, and behind the knees, especially in older children and adults (rash can be on the trunk of the body)

Hives

Hives (urticaria) are skin reactions that appear as itchy swellings and can occur on any part of the body. Hives can be caused by an allergic reaction, such as to a food or medication, but they also may occur in non-allergic people. Typical hive symptoms are:

• Raised red welts
• Intense itching

Allergic Shock

Allergic shock (anaphylaxis or anaphylactic shock) is a life-threatening allergic reaction that can affect a number of organs at the same time. This response typically occurs when the allergen is eaten (for example, foods) or injected (for example, a bee sting). Some or all of the following symptoms may occur:

• Hives or reddish discoloration of the skin
• Nasal congestion
• Swelling of the throat
• Stomach pain, nausea, vomiting
• Shortness of breath, wheezing
• Low blood pressure or shock

Shock refers to the insufficient circulation of blood to the body’s tissues. Shock is most commonly caused by blood loss or an infection. Allergic shock is caused by dilated and “leaky” blood vessels, which result in a drop in blood pressure.

How are Allergies diagnosed?

The history of your symptoms is important in diagnosing all allergies, including whether the symptoms vary according to time of day, season, exposure to pets and other potential allergens, and diet changes. Severe reactions often develop very quickly after exposure, such as eating nuts or getting stung by an insect.

Allergy testing may be required to determine if your symptoms are an actual allergy or caused by other problems. For example, eating contaminated food (food poisoning) may cause symptoms that resemble food allergies. Some medications (such as Aspirin, Ampicillin, and others) can produce non-allergic reactions, including rashes, that resemble drug allergies but are not true allergies.

Tests that may reveal the specific allergens include:

1) Skin testing — the most common method of allergy testing. This may include intradermal, scratch, patch, or other tests. Skin testing may even be an option for young children and infants, depending on the circumstances.

For assessing the presence of allergen-specific IgE antibodies, allergy skin testing is preferred over blood allergy tests because it is more sensitive and specific, simpler to use, and less expensive. Skin testing is also known as “puncture testing” and “prick testing” due to the series of tiny puncture or pricks made into the patient’s skin. Small amounts of suspected allergens and/or their extracts (pollen, grass, mite proteins, peanut extract, etc.) are introduced to sites on the skin marked with pen or dye (the ink/dye should be carefully selected, lest it cause an allergic response itself). A small plastic or metal device is used to puncture or prick the skin. Sometimes, the allergens are injected “intradermally” into the patient’s skin, with a needle and syringe. Common areas for testing include the inside forearm and the back. If the patient is allergic to the substance, then a visible inflammatory reaction will usually occur within 30 minutes. This response will range from slight reddening of the skin to a full-blown hive (called “wheal and flare”) in more sensitive patients. Interpretation of the results of the skin prick test is normally done by allergists on a scale of severity, with +/- meaning borderline reactivity, and 4+ being a large reaction. Increasingly, allergists are measuring and recording the diameter of the wheal and flare reaction. Interpretation by well-trained allergists is often guided by relevant literature. Some patients may believe they have determined their own allergic sensitivity from observation, but a skin test has been shown to be much better than patient observation to detect allergy.

If a serious life threatening anaphylactic reaction has brought a patient in for evaluation, some allergists will prefer an initial blood test prior to performing the skin prick test. Skin tests may not be an option if the patient has widespread skin disease or has taken antihistamines sometime the last several days.

2) Blood test — also called RAST (radioallergosorbent), this measures the levels of allergy antibody, IgE, produced when your blood is mixed with a series of allergens in a laboratory. If you are allergic to a substance, the IgE levels may increase in the blood sample. The blood test may be used if you have existing skin problems like eczema, if you’re on medications that are long-acting or that you cannot stop taking, if you have a history of anaphylaxis, or if you prefer not to have a skin test.

3) “Use” or “elimination” tests — suspected items are eliminated and/or introduced while the person is observed for response to the substance. This is often used to check for food or medication allergies.

4) Eyelid — Occasionally, the suspected allergen is dissolved and dropped onto the lining of the lower eyelid (conjunctiva) as a means of testing for allergies. (This test should only be done by a physician, never the patient, since it can be harmful if not done properly.)

5) Reaction to physical stimuli — heat, cold, or another stimulant is applied and the patient is observed to see whether they have an allergic response.

Other tests that may reveal allergies include:

• Antibody/immunoglobulin (particularly IgE) levels — when these are elevated, it indicates a “primed” immune system.
• CBC — may reveal an increase in eosinophils.
• Complement levels — may be abnormal.

How are Allergies treated?

The goal is to reduce the symptoms caused by inflammation of the affected tissues. Of course, the best “treatment” is to avoid what causes your allergies in the first place. It may be impossible to completely avoid everything you are allergic to, but you can often take steps to reduce your exposure. This is especially important for food and drug allergies.

Medications that can be used to treat allergies include the following:

• Short-acting antihistamines – these are generally non-prescription and often relieve mild-to-moderate allergy symptoms but they can cause drowsiness. In addition, these antihistamines can blunt learning in children (even in the absence of drowsiness). An example is diphenhydramine. One formerly prescription medication, loratadine (Claritin), is now available over the counter. It does NOT tend to cause drowsiness or affect learning in children.
• Longer-acting antihistamines cause less drowsiness and can be equally effective; usually they do not interfere with learning. These medications, which require a prescription, include fexofenadine (Allegra) and Cetirizine (Zyrtec).
• Nasal corticosteroid sprays are very effective and safe for people with symptoms not relieved by antihistamines alone. These prescription medications include fluticasone (Flonase), Mometasone (Nasonex), and Triamcinolone (Nasacort AQ).
• Decongestants may also be helpful in reducing symptoms such as nasal congestion. Nasal spray decongestants should not be used for more than several days because they can cause a “rebound” effect and make the congestion worse. Decongestants in pill form do not cause this effect.

• Leukotriene inhibitors — Montelukast (Singulair) is a prescription medicine approved to help control asthma and to help relieve the symptoms of seasonal allergies.

The most appropriate medication depends on the type and severity of symptoms. Specific illnesses that are caused by allergies (such as asthma, hayfever, and eczema) may require other treatments.

Allergy shots (immunotherapy) are occasionally recommended if the allergen cannot be avoided and symptoms are hard to control. Regular injections of the allergen are given, with each dose slightly larger than the previous dose. Allergy shots keep your body from over-reacting to the allergen. They do not work for everybody and require frequent visits to your doctor.

Severe reactions (Anaphylaxis) require epinephrine, which can be life saving when administered soon after exposure by patients themselves.

Drugs rating:

Where are allergens?

Everywhere…

We have seen that allergens are special types of antigens that cause allergic reactions. The symptoms and diseases that result depend largely on the route of entry and level of exposure to the allergens. The chemical structure of allergens affects the route of exposure. Airborne pollens, for example, will have little effect on the skin. They are easily inhaled and will thus cause more nasal and lung symptoms and limited skin symptoms. When allergens are swallowed or injected they may travel to other parts of the body and provoke symptoms that are remote from their point of entry. For example, allergens in foods may prompt the release of mediators in the skin and cause hives.

We will assume that allergens are defined as: the source of the allergy producing substance (for example, cat), the substance itself (cat dander), or the specific proteins that provoke the immune response (for example, Feld1). Feld1, from the Felis domesticus (the domesticated cat), is the most important chemical allergen in cat dander.

Allergens may be inhaled, ingested (eaten or swallowed), applied to the skin, or injected into the body either as a medication or inadvertently by aninsect sting.

In the Air We Breathe

Breathing can be hazardous if you are allergic. Aside from oxygen, the air contains a wide variety of particles; some toxic, some infectious, and some “innocuous,” including allergens. The usual diseases that result from airborne allergens are hay fever, asthma, and conjunctivitis. The following allergens are usually harmless, but can trigger allergic reactions when inhaled by sensitized individuals.

• Pollens: trees, grasses, and/or weeds
• Dust mites
• Animal proteins: dander, skin, and/or urine
• Mold spores
• Insect parts: cockroaches

In What We Ingest

When foods or medications are ingested, allergens may gain access to the blood stream and become attached to specific IgE on cells in remote sites such as the skin or nasal membranes. The ability of allergens to travel explains how symptoms can occur in areas other than the gastrointestinal tract. Food allergy reactions may begin with tongue or throat swelling and may be followed by tingling, nausea, diarrhea, or stomach cramps. Nasal breathing difficulties or skin reactions may also be seen. The two main allergen groups that are ingested are:

• Foods
• Drugs (when taken by mouth): for example, antibiotics and aspirin

Touching Our Skin

Allergic contact dermatitis is an inflammation of the skin that is caused by a local allergic reaction. The majority of these localized skin reactions do not involve IgE, but are caused by cells of inflammation. The rash produced is similar to that of a poison ivy rash. It should be noted that when some allergens (for example, latex) come into contact with the skin, they are absorbed by the skin and can also potentially cause reactions throughout the body, not just the skin. For most people, however, the skin is a formidable barrier that can be only locally affected. Examples of allergic contact dermatitis include:

• Latex (causes IgE and non-IgE reactions)
• Plants (poison ivy and oak)
• Dyes
• Chemicals
• Metals (nickel)
• Cosmetics

Allergic contact dermatitis does not involve IgE antibody, but involves cells of the immune system which are programmed to react when triggered by a sensitizing allergen. Touching or rubbing a substance to which you were previously sensitized can trigger a skin rash.

Injected into Our Body

The most severe reactions can occur when allergens are injected into the body and gain direct access to the blood stream. This access carries the risk of a generalized reaction, such as anaphylaxis, which can be life-threatening. The following are commonly injected allergens that can cause severe allergic reactions:

• Insect venom
• Medications
• Vaccines (including allergy shots)
• Hormones (for example, insulin)