Patient.co.uk defines an itchy rash with white bumps as acute urticaria, or hives. Typically, the rash develops from an allergic reaction to a food or medicine, or in response to exercise or heat. The itchy wheals or bumps that develop beneath the skin can either be red or white.
According to Patient.co.uk, acute urticaria usually lasts no longer than 24 to 48 hours, and it is not considered to be serious. Antihistamines, such as Zyrtec, are suggested for the itching.
In some cases, symptoms such as swelling of the throat and tongue appear along with hives. The swelling can become bad enough to cause the sufferer problems with breathing. The trigger for the rash is often brought about by the chemical histamine, which causes the rash to itch.
Patient.co.uk adds that hives that appear because of food allergies may result from the consumption of shellfish, chocolate, food additives, eggs, citrus or nuts. In some cases, an allergy to a medicine, such as an anti-inflammatory pain reliever, aspirin or penicillin may trigger a reaction.
A viral infection may also cause hives to appear. Some people may experience acute urticaria if their skin is exposed to products such as latex, cosmetics or ointments, or if they come into contact with certain plants.