Causes and Risk Factors for Hives
Hives usually are caused by an allergic reaction. However, in some cases, there is no clear cause for the rash. Urticaria can result when certain skin cells (called "mast cells") release histamine or other chemicals into the blood. These substances may cause blood vessels to leak fluid and hives to form.
People with a family history of hives and those who have had a previous allergic reaction are at increased risk for developing urticaria.
Hives can be triggered by the following:
- Allergies (e.g., to soap, cosmetics, cleaning agents, or detergents)
- Blood transfusions or blood products
- Emotional stress
- Environmental factors (e.g., sunlight, heat, cold, water)
- Exercise or physical exertion
- Food additives or preservatives
- Food allergies (e.g. to eggs, milk, berries, shellfish, tomatoes, nuts, or chocolate)
- Infections (e.g., viral illnesses, colds, hepatitis, other bacterial and fungal infections) Insect bites and stings
- Medications (e.g., antibiotics, nonsteroidal anti-inflammatory drugs [NSAIDs], laxatives, vitamins, herbal and diet supplements, sedatives, tranquilizers, diuretics, pain medications, eye drops, ear drops)
- Pressure (e.g., from tight clothing or sitting for long periods)
- Underlying health conditions (e.g., thyroid disease, lupus)