Hives When Sick: What to Know

Hives are raised, itchy welts that can appear in different places and fade while new ones arise. A viral or other infection may activate immune cells in the skin. A newly started medicine, including one used for the illness, can also be responsible. The timing of the first welts matters: record the illness symptoms, medicines, supplements, and foods taken before the rash appeared.

Hives can occur with a broader [Skin Rash](/symptoms/skin-rash/) or [Itchy Skin](/symptoms/itchy-skin/). Hives alone do not establish the cause, so a clinician may ask about the pattern, duration, and any previous episodes.

Keep the skin cool, wear loose clothing, and avoid scratching or hot showers while the welts are active. Do not stop a prescribed medicine without medical advice, but contact the prescriber promptly if the rash began after a new dose. A pharmacist or clinician can advise whether an [Antihistamine Treatment](/treatments/medical-dermatology/oral-antihistamine-therapy/) is suitable. Take a photo when the welts are visible and note whether each one fades within a day.

Get emergency help for trouble breathing, wheezing, faintness, confusion, or swelling of the lips, tongue, throat, or face. This may involve [Angioedema](/conditions/angioedema/) and can affect the airway. Seek same-day medical advice if the rash is rapidly spreading, follows a new medicine, comes with severe illness, or includes painful skin, blisters, mouth sores, or skin peeling.

Ask which trigger best fits the timing, whether any medicine should be changed, how to use an antihistamine safely, and what symptoms should prompt emergency care. Mention previous reactions and bring a complete medicine list.