Food allergy may present with a wide array of signs and symptoms. (The term present is doctor lingo for how a condition shows up in your body.) Food reactions typically involve the following three major organ systems in your body along with a fourth system that plays a role in severe reactions:

• Skin, such as hives or eczema
• Gastrointestinal tract, including nausea, stomach upset, and diarrhea
• Respiratory tract, including rhinitis (sneezing, runny nose) and difficulty breathing (or asthma)
• Cardiovascular system, sometimes involved in severe reactions

Some reactions are isolated to a single system, such as hives on the skin, while others may involve multiple systems, as sometimes occurs in an anaphylactic reaction. This myriad of presentations is one of the many reasons why some food allergies are so difficult to diagnose.

A food allergy can literally get under your skin. Skin reactions are the most common manifestations of food allergy. Symptoms, such as hives, may occur very acutely or as a much more chronic, low-grade condition.

Eczema (or atopic dermatitis) is a chronic skin condition characterized by extreme dryness and itchiness. It typically begins early in life and hits its peak prevalence at about one year of age. At that point, 15 to 20 percent of all one-year-olds have some degree of eczema, ranging from extremely mild to involving only tiny areas of skin to extremely severe cases involving the entire body.

Tracing eczema back to a food allergy requires some savvy detective work for various reasons.

• Eczema may not involve food allergy. Your doctor may not even suspect food allergy as the cause. Other factors that can contribute to eczema’s onset and severity include:

• Genetic susceptibility
• Heat
• Humidity
• Certain types of clothing
• Soaps or detergents

• Food reactions that trigger eczema are typically low-grade and difficult to identify.

• Reactions may be delayed by several hours.

• Symptoms can wax and wane over time, due to temperature, humidity, and environmental irritants.

• Foods that typically trigger eczema are common foods eaten on a very regular basis. If you drink milk or eat wheat several times a day, detecting any clear connection between a specific food and your eczema symptoms can be nearly impossible.

Based on a large number of studies, we know that food allergy is at the root of about 40 percent of all cases of children with moderate to severe eczema. This means that at least 50 percent of children with eczema, including some with severe eczema, do not have food allergy.

For the remainder, however, identifying the underlying food allergy and restricting the allergenic foods often leads to a marked improvement in symptoms. And given that eczema is an extraordinarily uncomfortable condition due to the severe itching that it creates, anything that makes you more comfortable is of extreme value.

When food allergy is involved in eczema, the five most common food allergens are the prime suspects — egg, milk, peanut, soy, and wheat. Other foods can certainly be involved, but these top five are the most important to remember.

In fact, if a child with eczema tests negative to these five foods by either skin testing or blood testing, the likelihood of any food allergy is extremely low. Once you and your doctor have accomplished the daunting task of tracing your eczema to a food allergy, you can find symptomatic relief later.

Hives

Hives (also known as urticaria) are itchy, raised splotches on the surface of your skin. About 20 times itchier than a mosquito bite, hives make you want to tear off your clothes and then your skin. When most folks have their first encounter with hives, they assume the condition is caused by something they ate.

In most cases, however, hives are the result of other conditions:

• Viral illness: In many cases, a viral illness can trigger an outbreak of hives.

• Anxiety: When some people get real nervous, they get hives. This condition is called cholinergic urticaria.

• Heat or Cold: Cholinergic urticaria can also result from an increase in a person’s core body temperature or other temperature extremes. Some people can’t even perform their normal exercise routine without breaking out in hives.

• Vibration: Any vibration against the surface of the skin, even from clothing rubbing against it, can trigger a bout of hives in those prone to cholinergic urticaria. This is rare, indeed. In fact, I’ve never seen a case of vibratory urticaria.

• Chemical reaction: A reaction to penicillin or other medications can cause hives.

If you haven’t eaten anything remotely suspicious in the few hours before experiencing hives, you can safely assume that your hives have nothing to do with a food allergy. Determining the cause of a random outbreak is usually impossible.

If, however, hives occur shortly after eating a new food, food allergy could certainly be the cause, especially if you just ate one of the more highly allergenic foods. A typical scenario is a baby who develops hives after his first taste of yogurt or scrambled eggs or peanut butter.

When hives are due to food allergy they typically occur almost immediately (within 30 minutes) after eating the food and rarely beyond four hours after eating a suspicious food. If you ate shrimp on Saturday and got hives on Monday, it’s not the shrimp. A case of hives is not, in itself, serious, but it may be a sign of something more serious now or in the future.

Keep the following important points in mind:

• Hives accompanied by other symptoms including vomiting or restricted breathing may be a sign of the onset of a severe allergic reaction. The more different parts of your body that are involved in a food reaction, the more dangerous it may be.

• A mild outbreak of hives can indicate the possibility of more severe allergic reactions in the future. This doesn’t guarantee that your next reaction will be worse, but you should certainly be prepared for that possibility. When I teach doctors about food allergy, I always tell them that just because that first reaction caused only hives, you have no guarantee that a future reaction will not be more severe.

If you’re experiencing repeated bouts of hives and are unsure of the reason, try keeping a food diary for a week or two to see if you can trace your recurring hives to a specific food. While you’re logging your encounters with hives, consult your doctor and draw up an emergency plan just in case your next reaction is more severe.

Angioedema

Angioedema means swelling. Although it may occur alone, it most often accompanies hives. In fact, many doctors think of angioedema as hives to the nth degree, although hives tend to be more localized. During a reaction, angioedema can produce a wide range of symptoms:

• Welts, particularly on the face and around the eyes.

• Swollen lips.

• Intestinal swelling, often resulting in painful stomachache.

• Restricted or obstructed breathing, due to swelling of the airway. This is the most serious manifestation of angioedema, because the swelling can completely block the airway. Keep in mind that your windpipe is less than an inch in diameter and considerably narrower in children — a little swelling can easily pinch it shut. Angioedema’s ability to obstruct breathing is the most common cause of life-threatening and fatal food reactions.

Patients often wonder if having angioedema externally, such as a swollen eye, indicates some internal swelling that they can’t observe. External swelling can occur without internal swelling, but even so, when you observe significant external swelling, you need to be concerned about the possibility of swelling in the airway.

Respiratory Reactions

Food reactions can involve the airway anywhere from the tip of the nose to the bottom of the lungs, resulting in any or all the following symptoms:

• Nasal congestion or runny nose.

• Swelling of the throat or airway.

• Swelling of the bronchial tubes and even smaller airways in the lungs. When this occurs, the asthma-like symptoms occur as a result of a combination of airway swelling, muscle constriction, and mucus production. Asthmatic patients are much more likely to have these lower respiratory difficulties as part of a food reaction. In fact, patients with asthma are at far greater risk of having life-threatening or fatal allergic reactions because of this lower airway component.

When the lower airway — the throat and lungs — is involved in an allergic reaction, immediate administration of epinephrine is critical. Antihistamines have virtually no effect on these reactions. Asthma medications may be effective or completely useless, so don’t rely on them. Epinephrine is king.

Although acute food reactions often involve the respiratory tract, chronic congestion and other chronic respiratory conditions, such as asthma, are rarely the work of a food allergy.

So, if you have chronic nasal congestion or asthma, without other food allergy symptoms, such as hives, eczema, or intestinal problems, your doctor is unlikely to suspect or test for food allergy as a cause. Environmental allergies become the prime suspect in these cases.

Gastrointestinal Reaction

The most obvious victim of a food reaction is your gastrointestinal (GI) track — your digestive system, which starts in your mouth and ends in the waste canal.

Because this system processes everything you eat and drink, you’d suspect it to suffer during a food allergy reaction, and it often suffers plenty. Like skin reactions, GI reactions may range from very acute to very chronic. Acute food reactions that attack the GI tract typically occur within moments after eating the offending food, and often produce the following symptoms:

• Itching in the mouth
• Swelling of the tongue
• Nausea
• Vomiting
• Abdominal pain
• Diarrhea (sometimes)

Although these symptoms can occur alone, they’re often accompanied by other symptoms, such as hives and angioedema. Chronic gastrointestinal symptoms behave much more like eczema — these symptoms indicate a more delayed and lower-grade reaction than in acute cases. Symptoms include the following:

• Gastroesophageal reflux. In infants with reflux, food allergy plays a role in up to one-third of cases and may be the sole cause of the reflux. In infants who can’t seem to hold down their food, doctors should at least consider the possibility of food allergy. Food allergy is less likely in older children, adolescents, or adults with reflux, although it certainly occurs occasionally and should not be overlooked.

• Persistent abdominal pain. A chronic stomachache can be the sign of a food allergy. Of course, it can also be a sign of eating too much junk food. Have it checked out.

• Weight-loss and poor growth in children. These are usually related conditions that arise as a result of chronic gastrointestinal reactions, because patients may be eating less and be unable to fully absorb nutrients due to chronic gastrointestinal inflammation.

• Constipation. Although food allergy can cause constipation, it’s not common. If you have a difficult case of constipation that doesn’t respond to other treatments or your constipation is accompanied by other food allergy symptoms, such as hives or eczema, you may want to be tested for food allergy. Otherwise, the cause is probably something else.

Uncovering Anaphylaxis

Anaphylaxis (often called anaphylactic shock, but I’ll get to that later) is an allergic reaction that involves multiple organ systems. If you experience symptoms in any two or more of the following organ systems, you’re experiencing anaphylaxis:

• Skin: The most common symptoms of anaphylaxis are urticaria (hives) and angioedema (swelling of the tissues under the skin), but these symptoms are absent in up to 20 percent of anaphylactic reactions.

• Respiratory tract: Respiratory symptoms occur in about 50 percent of people who have anaphylaxis and are especially common in people who also have asthma. Low blood pressure can cause lightheadedness, dizziness, tunnel vision, and loss of consciousness (passing out).

• Gastrointestinal tract: Gastrointestinal symptoms occur in 30 percent of people.

• Cardiovascular system: Anaphylactic shock (extremely low blood pressure) occurs less commonly but may be increasingly common with age, occurring in up to 30 percent of adults who have a reaction.

Anaphylaxis isn’t always anaphylactic shock. In medical circles, shock refers to a drop in blood pressure to a dangerously low level. You can experience anaphylaxis with or without the shock (the dangerous drop in blood pressure). Anaphylaxis typically unfolds according to one of the following three scenarios:

• Uniphasic: A single wave of symptoms.
• Biphasic: In about a third of the cases, the reaction appears to resolve but recurs one to eight hours later.
• Protracted: Rarely, a pattern referred to as protracted anaphylaxis occurs, with signs and symptoms persisting for up to 48 hours despite treatment.

Thankfully, not all anaphylaxis is severe and life-threatening. Some reactions even resolve on their own without treatment, but that’s impossible to predict, so you must treat all anaphylactic reactions promptly with epinephrine.

Whenever the core of your being — your heart and all the pipelines through which it pumps your blood — is involved in a reaction, all sorts of really bad stuff can happen, and it can happen in a hurry:

• Hypotension: Hypotension (a drop in blood pressure) is the most common symptom. When your blood pressure drops, you often get dizzy, feel lightheaded, and sometimes pass out. An extreme drop in blood pressure results in anaphylactic shock.

• Heart arrhythmia: A heart arrhythmia is a variation in the beating of your heart — beating too fast, too slow, or irregularly.

• Heart attack: A severe food allergy reaction can give you a heart attack.

In children and young adults, anaphylactic shock is relatively uncommon even with the most severe reactions, because their cardiovascular system is so resilient. This does not mean, however, that younger people are immune to severe anaphylaxis. Anaphylaxis in younger people typically results in breathing difficulty — a constricted or blocked airway that causes the fatal and near fatal reaction.

In a fatal reaction, the heart stops only because the body eventually runs out of oxygen. Anyone who has food allergies should remain on the lookout for the signs and symptoms that presage a severe reaction, but some people may need to remain more vigilant than others. The following factors contribute to increasing your risk for experiencing a severe or fatal anaphylactic reaction.

• Naming the high-risk foods: While any food allergen can cause anaphylaxis, a few are particularly skilled at doing so. The most sinister of the bunch are peanuts, tree nuts, sesame, and shellfish. Peanuts and tree nuts alone are responsible for 80–90 percent of all fatal reactions.

Other foods, including milk, egg, and wheat can cause severe reactions, as well. In fact, I see many patients with reactions to these foods that are just as severe as the worst peanut reactions. The reality though is that while most people with peanut and tree nut allergy are at risk for severe reactions, a far lesser proportion of people allergic to most other foods share the same risk.

• Increasing the severity with asthma: People with asthma are more likely to experience anaphylaxis and to have more severe respiratory problems during anaphylaxis. The combination of food allergy (especially to peanuts and tree nuts) and asthma seems to put people at risk for dangerous attacks.

• Repeating bouts of anaphylaxis: People who’ve had an anaphylactic reaction in the past are at increased risk of future anaphylactic reactions. However, everyone with anaphylaxis has had their first reaction once, so just because a food allergy has not previously caused anaphylaxis does not place you in the low-risk category.

No doubt about it — food allergies can cause a wide variety of symptoms ranging from a mild tummy ache to a major system shutdown, but food allergy can’t be blamed for every medical condition known to humankind. Unfortunately, people commonly suspect food allergy as the root cause of a host of maladies.

The risk involved in mistakenly suspecting food allergy as the cause of other medical and behavioral issues is that the time, energy, and resources you spend in pursuing an unlikely cause is wasted. You’re better off seeking help from specialists who treat these conditions.

Medical wisdom advises doctors that “When you hear hoof beats think of a horse rather than a zebra.” In other words, suspect the most common causes first before testing for causes that are less likely.

Food allergies, for example, can cause other conditions — arthritis, inflammatory bowel disease, migraine headaches, or recurrent ear infections, but when these conditions arise, you need to investigate their more common causes first before suspecting food allergies.

Only after ruling out more likely causes (or if these conditions are accompanied by other symptoms that can be more readily attributed to food allergy) should you suspect food allergy as the cause.

Some people want to blame everything on a food allergy, including psychiatric and behavioral disorders, such as attention deficit disorder, hyperactivity, and depression. A quick search on the Internet revealed over four million Web pages dealing with the relationship of attention deficit disorder and hyperactivity with food allergy.

These conditions, however, are rarely, if ever, due to a true food allergy. In caring for patients with food allergy, I’ve learned to never say “never,” so I’m not claiming that behavioral disorders and other conditions can’t possibly be related to food allergy, but the likelihood is extremely low.

I see many families who are hoping to find an easy and quick fix to significant behavioral issues by first exploring the possibility of a food allergy. In doing so, their children might be missing out on some wonderful therapies that are available elsewhere.