Healthy skin is good at protecting the body from the outside world. The combination of sebum (the skin's natural oil) and low levels of perspiration produce an "acid mantle," an acidic barrier that discourages aggressors, such as viruses and bacteria, from invading the body. When the acid mantle is disrupted, the skin's barrier function is compromised and a rash can result. Not all rashes are caused by a break in the acid mantle, however. Genetic factors, medication, disease and certain allergies can also cause rashes.
Tinea
Tinea is a global name for a host of skin rashes caused by a fungal infection of the uppermost layer of skin. Tinea, or ringworm, can appear anywhere on skin, though when it appears in specific areas of the body, the outbreak is differentiated by a second word describing the location. Tinea pedis refers to an outbreak on the feet, which is commonly athlete's foot. Tinea capitis refers to an outbreak on the scalp, while tinea cruris occurs in the groin area, on the buttocks and on the upper thighs. It is commonly referred to as jock itch.
Ringworm rash on the body appears in a characteristic ring shape with an area of healthy skin in the center. As the infection spreads, concentric circles appear around the original infection. On the scalp, the fungal infection appears in circular patches that slowly grow in size and that can cause hair to break off near the scalp. Scalp ringworm spreads easily and can be contracted through person-to-person contact or through contact with an infected pet.
Like many fungi, the fungus that causes ringworm thrives in dark, moist, warm areas of the body. Areas where sweat accumulates, within creases in the skin and between the toes are ideal environments for fungal proliferation.
Eczema
Eczema is a common, chronic skin condition characterized by patches of itchy skin. Scratching causes a red, inflamed rash to form. Crusting, weeping of the skin, blistering and the development of scaly flakes can accompany the rash. People in any age group can develop eczema, though it appears to have a genetic basis. When it appears in infants, food sensitivity can be the trigger. Foods that are associated with eczema outbreaks include milk products, shellfish and nuts. Contact with irritants can also trigger an outbreak. Contact with wool, soap, fragrances and dyes can trigger an outbreak in sensitive individuals.
Dermatitis
Rashes often develop after contact with an irritant or with an allergen. Irritant contact dermatitis occurs after contact with an irritating substance. The contact can be long-term, with the rash developing over time, or it can be an immediate reaction to one-time contact with a harsher irritant, such as contact with certain acids. Allergen-contact dermatitis, on the other hand, is a rash that occurs after an individual has come into contact with a substance to which she is allergic, or to which she has developed an allergy. First-time contact with poison ivy, for instance, may not cause a rash reaction. Repeated exposure, however, can cause an individual to develop an allergy to the oils secreted by the leaves of the ivy and every contact after that will cause a red, itchy rash outbreak.
