Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Rash

What Is It?

A rash is a temporary eruption or discoloration of the skin and is often inflamed or swollen. Rashes come in many forms and levels of severity, and they last for different amounts of time. Some common causes of rashes include:

• Infections — This broad category covers a wide range of illnesses, including:

  • Viral infections, such as measles, rubella, roseola, fifth disease, varicella zoster, herpes or shingles

  • Bacterial infections, such as impetigo, scarlet fever or Lyme disease

  • Fungal infections, such as jock itch (a fungal infection in the groin region)

  • Many others

• Allergic reactions — These can be triggered by:

  • Medications, including antibiotics, seizure medications and diuretics

  • Topical skin products, such as cosmetics, perfumes or skin creams

  • Foods, especially peanuts, seafood and eggs

  • Insect stings (including bees, wasps and hornets)

• Local irritants — This category includes diaper rash (caused by prolonged skin contact with urine and stool) and rashes caused by contact with harsh chemicals, such as laundry soaps and fabric softeners.

• Poisonous plants — Poison ivy, poison oak and poison sumac share a highly allergenic sap resin that can cause allergic rashes in 70% of people exposed to it.

• Autoimmune disorders — This category includes systemic lupus erythematosus (SLE or lupus), dermatomyositis and scleroderma, disorders in which the body's immune defenses mistakenly attack healthy areas of the body, including the skin.