Medications, poor digestion, or illness may also cause rashes or hives. One of the most common forms of a rash is contact dermatitis, which is caused when a substance of some sort irritates the skin. A more severe reaction may cause swelling, redness, and larger blisters.

Rashes can be caused by many things, including poison ivy, poison oak, soaps, detergents, shampoos, perfumes, lotions, a latex allergy, and a food allergy.

They may also occur from viral infections such as shingles, fungal infections, acne, eczema, psoriasis, rosacea, Lyme disease, but bites, or heat exposure.