Breaking out in hives (also called urticaria) occurs when the body releases histamine and other chemicals into the skin due to an allergic reaction or other triggers. Common reasons for hives include allergies to foods (like peanuts, shellfish), medications, insect bites, or environmental exposures such as pollen, cold or heat, sunlight, or pressure on the skin. Other causes can be infections (viral or bacterial), exercise, sweat, stress, or underlying medical conditions like autoimmune diseases (lupus, thyroid disorders). Sometimes hives occur without a clear cause, especially if they are chronic or recurrent.

Common Causes of Hives

• Allergic reactions to foods, medications, insect stings, or chemicals.
• Environmental factors: cold or hot temperatures, sunlight, water, pressure, vibration.
• Infections: colds, flu, bacterial infections.
• Physical triggers: exercise, sweating, tight clothing.
• Stress and emotional factors.
• Underlying illnesses: autoimmune disorders such as lupus or thyroid disease.

What Happens in the Body

Hives result from the release of histamine into the bloodstream when the immune system perceives a threat. This causes red, itchy welts on the skin that can occur anywhere on the body.

When to See a Doctor

If hives last more than a few days, keep recurring, or are accompanied by symptoms like difficulty breathing, swelling of the face or throat, dizziness, or loss of consciousness, immediate medical attention is essential. For chronic or unexplained hives, a healthcare provider can help diagnose underlying causes and recommend treatment options such as antihistamines. This information comprehensively covers why someone might break out in hives, including common triggers and when to seek help.