Allergy to shellfish, including crab, is self-reported by 2.5 percent of American adults and 0.5 percent of American children, according to a December 2010 report published in “The Journal of Allergy and Clinical Immunology.” Considered a life-long allergy, symptoms are varied --ranging from mild to life-threatening -- and seafood allergy symptoms tend to be more severe compared to other food allergens. Along with eating crab, touching this shellfish or even inhaling cooking vapors or crab particles can induce an allergic response in susceptible people.
Common Allergy Symptoms
An allergic reaction occurs when a person with an allergy is exposed to a specific protein, or allergen, and the subsequent immune response releases histamines, which produces the classic allergy symptoms. Crab allergy symptoms are not different from the allergic response to any shellfish, and common symptoms include:
- Swelling of the lips, mouth, throat or face, or a tingling sensation in the mouth.
- Skin effects such as hives -- red, swollen and itchy skin welts.
- Gastrointestinal symptoms including vomiting, stomach cramps, indigestion or diarrhea.
- Respiratory problems including cough, wheezing or shortness of breath.
For those allergic, shellfish contains potent allergens, and symptoms can occur from skin contact or inhalation. When crab is processed or cooked in quantity, airborne allergens can be abundant, and those allergic often have respiratory or skin-related symptoms. Occupational exposure in seafood processing plants is known to cause allergic response even in workers without prior allergies, according to a September, 2011 report in "Occupational and Environmental Medicine." Skin exposure is also common in employees working with crab, and allergic contact dermatitis -- an allergic reaction that causes a rash and skin lesions -- can occur in these workers.
While allergies and asthma are different conditions, both involve the respiratory system and are linked to an overreaction of the body’s immune response. So it may not be surprising that environmental and occupational exposure to crab or other seafood, as with seafood processing workers, may trigger asthma. Occupational asthma may also occur in restaurant workers as a result of airborne allergen exposure. Asthma symptoms include wheezing, chest tightness, difficulty breathing and cough. Symptoms can start minutes after exposure and clear up 1 to 2 hours after being away from the workplace, but symptoms may also be delayed for several hours after exposure.
Anaphylaxis is a severe, potentially deadly allergic reaction which can occur in people who have crab and other shellfish allergies. Symptoms of this life-threatening response are sudden and affect the entire body. Commonly, a drop in blood pressure occurs with flushed skin, rash, swelling of tissues and joints, wheezing, nausea, abdominal cramps, rapid pulse, convulsions and fainting. Persons allergic to crab require immediate medical attention with the onset of these symptoms.
According to an article published in the June, 2011 issue of "Clinical and Translational Allergy," crab and other shellfish allergies can be challenging to diagnose, as some seafood reactions can be triggered by marine toxins, bacteria, parasites or viruses -- yet cause symptoms similar to true allergic reactions. If you suspect you have an allergic reaction to crab, because of potential cross-reactions, avoiding other shellfish is prudent until you discuss your allergy management with your allergist. Keep in mind that even small amounts of crab -- whether consumed, airborne or via skin contact -- can cause a reaction in those who are allergic. Even when there is no obvious presence of crab in the dish, cross-contamination can occur at the time the food is processed, prepared or cooked. If you have a crab allergy, your allergist will guide you on home treatment, and when to seek urgent medical care. However, seek emergency medical care if you have any symptoms of anaphylactic shock.