There are many types of rashes, and MedicineNet.com reports that contact dermatitis and heat rash are two of the most common. Eczema and pityriasis rosea are other types of rashes, according to WebMD.
Contact dermatitis occurs when the skin comes into contact with an irritant or allergen, whether it's a substance or chemical, states MedicineNet.com. Some examples include jewelry that contains nickel and poison oak or ivy. The resulting rash may ooze or weep occasionally.
A heat rash is inflammation of the skin when the sweat ducts become blocked, occurring often in hot, humid environments, explains MedicineNet.com. It most likely appears on the upper chest or neck, around the groin, in elbow creases and under the breasts. Heat rash looks like a cluster of small, red blisters or pimples.
Eczema generally describes many skin conditions, and atopic dermatitis is the most common type, reports WebMD. The cause is unknown, and the rash may appear on the scalp, face, neck, elbows or knees. The rash causes redness, itching, oozing blisters, infections if the skin breaks, and dry, crusted or scaly skin.
A virus is believed to cause pityriasis rosea, a common rash among young adults that begins as one large patch on the skin, says PubMed Health. Several days later, more oval-shaped rashes flare up on the chest, arms, back and legs. The patches are often pale red or pink, and they may itch, appear scaly or look like a Christmas tree.