Shellfish allergy symptoms typically develop within minutes after ingesting seafood or shellfish. They can last from several hours to a few days, depending on the severity of the reaction and the treatment you have.

Mild symptoms of shellfish allergies, such as hives or gastrointestinal symptoms, may resolve within a few hours, especially if you take an antihistamine like loratadine. Severe reactions, like anaphylaxis, require immediate medical care and may require more extended recovery periods.

Immediate medical care is essential if you experience shellfish allergy symptoms that may indicate anaphylaxis, a severe and potentially life threatening allergic reaction. These symptoms include:

  • difficulty breathing or swallowing
  • itching, swelling, or tightness of the throat
  • severe swelling of the mouth, tongue, and eyes
  • sudden changes in blood pressure
  • lightheadedness or dizziness
  • fainting

Symptoms of anaphylaxis can worsen quickly, so don’t wait to see whether they resolve on their own. You may need an epinephrine injection or other urgent care.

If your symptoms of shellfish allergy are mild and do not worsen with time, immediate medical care may not be required. Mild symptoms may include diarrhea, headache, upset stomach, and hives.

If you’ve had an allergic reaction to shellfish or seafood, even if mild, you may want to consult a healthcare professional for allergy testing.

Proper diagnosis may avoid future emergencies, as allergic reactions may change in severity. They may also guide you about what to do if you ever have another allergic reaction to shellfish or other foods, and whether oral antihistamines are indicated in your case.

If you suspect a shellfish allergy or any other type of allergy, check out our guide to visiting an allergist.