Rash is a general medical term used to describe skin inflammation with red eruptions, and skin irritation is a rash if it includes inflammation and red eruptions. The most common causes of rashes are viral, bacterial or fungal infections, according to MedicineNet.com.
Herpes simplex and measles are rashes caused by viral infections. Herpes simplex is a pus-filled red bump at the corner of the mouth. Measles is a systemic infection that causes a rash over a large portion of the body. The most common bacterial infections that cause rashes are impetigo and folliculitis. Both conditions result from staph or strep infections and include pus-filled bumps as part of the rash. Doctors use oral antibiotics to treat these conditions. A person can contract a fungal infection that causes a rash from public areas such as a pool or locker room or from other household members. Doctors treat this type of rash with over-the-counter topical antifungal creams, according to MedicineNet.com
Contact dermatitis occurs when a person's skin contacts an irritating substance. A person develops redness or small red bumps in mild cases and swelling or blisters in severe cases. Contact dermatitis develops most often after encountering poisonous plants, soaps, jewelry, fabrics or latex, reports WebMD.
A person can also develop a rash from extreme hot or cold weather, an insect bite, parasites, or emotional stress. Toxic epidermal necrolysis occurs as a rare side effect of sulfa drugs and appears as a generalized red rash that produces large areas of exposed tissue, WebMD explains. A chronic rash may indicate acne, eczema or psoriasis.