Rash: Causes

What causes rashes?

Rashes can be caused by a wide variety of diseases and conditions, such as infection, inflammation, allergic reaction, parasite and insect bites, and autoimmune processes.

Infectious causes of rashes

A rash may be caused by an infection including:

• Bacterial infection

• Chickenpox

• Fungal infection

• Herpes

• Impetigo

• Measles

• Meningitis

• Ringworm

• Shingles

• Staph infection

• Strep infection

• Viral infection

Allergic causes of rashes

A rash may be caused by an allergic reaction including:

• Allergens, such as animal dander

• Contact dermatitis

• Drug reaction

• Dust or mold allergy

• Eczema

• Food allergies

• Hives

• Poison ivy, poison oak, or poison sumac

• Skin allergies

Autoimmune causes of rashes

A rash may be caused by an autoimmune response including:

• Psoriasis

• Systemic lupus erythematosus

• Vasculitis

Parasites, insects and arachnids that cause rashes

A rash may be caused by parasites, insects or arachnids including:

• Bedbugs

• Fleas

• Head lice or pubic lice

• Mosquitoes

• Scabies

• Ticks

Other causes of rashes

A rash may also be caused by problems in body systems other than the skin including:

• Acne

• Anxiety

• Erythema multiforme

• Erythema nodosum

• Heat rash

• Methamphetamine abuse

• Stress

• Toxic epidermal necrolysis

Life-threatening causes of rashes

In some cases, a rash may accompany a serious or life-threatening condition that should be immediately evaluated in an emergency setting. These include:

• Allergic purpura

• Anaphylaxis

• Meningitis

• Severe allergic reaction

Questions for diagnosing the cause of a rash

To diagnose the underlying cause of a rash, your doctor or licensed health care practitioner will ask you several questions related to your symptoms. You can best help your health care practitioner in diagnosing the underlying cause of your rash by providing complete answers to these questions:

• Describe the rash. Where is it? What does it look like?

• Did the rash develop suddenly or slowly? Is it constant or intermittent?

• Does the rash occur with any particular activity, such as eating?

• What other symptoms are you having?

• Have you been in recent contact with any unusual or new substances or environments, such as poison ivy or new medications or food?

Provide your full medical history, including all medical conditions, surgeries and treatments, family history, and a complete list of the medications and dietary supplements that you take.

What are the potential complications of a rash?  

In some cases, a rash can lead to complications, especially if the itching is severe and leads to breakdown of the skin. Complications include:

• Bacterial or fungal infection of the skin

• Cellulitis (an infection of the skin and surrounding tissues caused by a growing bacterial or fungal infection)

• Open sores and lesions

• Permanent change in skin texture or scarring

• Permanent skin discoloration