Heat, allergens, infections, medications and disorders of the immune system are common causes of many types of rash, according to Mayo Clinic. Rashes vary in symptoms and appearance depending on the type.
Atopic dermatitis, also referred to as eczema, causes an inflammation of the skin, explains Mayo Clinic. It usually clusters in patches around the trunk of the body as well as on the face, neck and limbs. Contact dermatitis is caused by the skin making direct contact with an allergen, irritant or toxic chemical. When caused by exposure to chemicals, it takes the form of a scaly rash, which is generally dry and doesn't itch. If the rash is caused by contact with an allergen, it takes the form of itchy red bumps and blisters. Nickel metals, latex and poison ivy are common causes of this type of rash.
Reactions to medications such as antibiotics are a common cause of rashes, according to Mayo Clinic. Drug rashes appear as red spots that spread over time to cover large areas of the body, and they may worsen when exposed to sunlight. Heat rash is caused by an obstruction of sweat glands and tends to affect those in a hot, humid climate. It may form as clusters of small red bumps that have a prickly sensation, or it may take the form of clear bumps filled with fluid.
Other common rashes include rosacea, which causes small red or pus-filled bumps on the face, explains Mayo Clinic. Rosacea can be caused by certain foods, sun exposure, temperatures and skin products. A contagious fungal infection called ringworm appears as raised red rings on the skin. Ringworm can be caused by skin-to-skin contact with an individual who is infected as well as contaminated objects.