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Symptoms of a Crab Allergy

author image Grace Ibay
Grace Ibay has been a freelance writer and blogger since 2005, specializing in the medical sciences and health care. She worked at Johns Hopkins University and the National Institutes of Health as a research associate and has been published in various scientific journals. Ibay holds a master's degree in health science from Johns Hopkins University in Maryland.
Symptoms of a Crab Allergy
Pile of steamed crabs. Photo Credit Richard Gunion/iStock/Getty Images


Allergy to crab is one of the most common food allergies in adults. It causes some of the most severe allergic reactions, and is considered life-long. People who are allergic to crab usually also have allergies to other shellfish, reports the American Academy of Allergy, Asthma and Immunology, or AAAAI. It is also common for seafood dishes that do not contain crab to be cross-contaminated with crab allergens. Physicians might advise these patients to refrain from eating or handling other kinds of shellfish. Allergic reaction to crab can occur when people touch, eat or taste food with crab or when they breathe in cooking vapors. Symptoms of crab allergies range from mild to life-threatening.

Tingling in the Mouth

People who are allergic to crab may initially experience a tingling sensation in the mouth after eating crab. Even very small amounts of crab allergen may cause this sensation. 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.

Hives and Swelling

Individuals who have allergies to crab may experience symptoms related to hives. Hives are red, swollen and very itchy welts on the skin that last from 2 to 4 hours. Hives usually go away once the person stops handling or eating crabs. Angioedema, or excessive swelling of the lips, mouth or throat, may happen immediately after eating crabs, notes Dr. Lopata in the April 2010 issue of Clinical and Experimental Allergy. Swelling of the entire face or larger parts of the body may indicate a more serious reaction.


Eczema starts out as very small, pimple-looking bumps that become very itchy and dry. Scratching results in swollen, crusty, thick scaly rashes that become worse over time. Eczema frequently occurs in people who work in crab- or seafood-processing plants, or those who handle seafood in their workplace, according to Dr. Lopata.


Asthma may also develop when a crab-sensitive person touches, eats or inhales cooking vapors of food contaminated with crab. Asthmatic symptoms include wheezing, chest tightness, difficulty breathing and cough. Asthma may also occur in the workplace, such as processing plants or seafood restaurants. The Asthma and Allergy Foundation of America notes that wheezing can happen minutes after exposure and clear up 1 to 2 hours after being away from the workplace. A delayed asthmatic reaction may also occur 3 to 8 hours after exposure and flare up in the evenings. Patients with asthma or allergic reaction to crab should inform their doctor if they suspect work-related asthma.


Anaphylaxis is a severe, possibly deadly allergic reaction to crab and other shellfish. Anaphylaxis affects the entire body and causes blood pressure to drop. Symptoms are varied and may happen all at once: flushed skin, rash, swelling of tissues and joints, wheezing, nausea, abdominal cramps, rapid pulse, convulsions, and fainting. According to the AAFA, intense exercise after eating crab may cause anaphylaxis. Persons allergic to crab require immediate medical attention when symptoms of anaphylaxis begin to occur.

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