Introduction to Rashes

A rash is a change of human skin which affects colour, appearance or texture. A rash may be localized in one part of the body, or affect all the skin. Rashes may cause the skin to change color, itch, become warm, bumpy, chapped, dry, cracked or blistered, swell, and may be painful. The causes, and therefore treatments for rashes, vary widely. Diagnosis must take into account such things as the appearance of the rash, other symptoms, what the patient may have been exposed to, occupation, and occurrence in family members. The most common acute rashes tend to be due to infection, due to a reaction to something, or rashes that are a marker of something else going on in the body.

As such, a rash is not a specific diagnosis, instead it refers to any sort of inflammation and/or discoloration that distorts the skin’s normal appearance. Some common rashes include eczema, poison ivy, hives, and athlete’s foot, and I will look into more detail at some rashes later on in the post. Infections that cause rashes may be fungal, bacterial, parasitic, or viral. Over-the-counter products may be helpful treatments for many skin rashes, but, rashes lasting more than a few days that are unexplained should be evaluated by a doctor.

All rashes can be described in terms of the appearance of the lesions on the skin. The terms are used to describe the rash and not necessarily point to the diagnosis. The most common terms that are used are: macular (flat lesions), papular (raised lesions), vesicular (fluid filled blisters), urticaria (hives), petechiae (dark red spots that do not temporarily disappear when the skin is stretched or pressed on) and purpura (bruises). Now I am going to look into more detail at some common rashes (n.b. don’t use the following to self-diagnose):

  1. Atopic dermatitis, often called eczema, is a common disorder of childhood that produces red itchy, weeping rashes on the inner aspects of the elbows and in back of the knees as well as the cheeks, neck, wrists, and ankles. It is commonly found in patients who also have asthma and/or hay fever.
  2. Seborrheic dermatitis is the single most common rash affecting adults. It produces a red scaling often itchy eruption that characteristically affects the scalp, forehead, brows, cheeks, and external ears. In infants, it may involve and scalp (cradle cap) and diaper area.
  3. Contact dermatitis is a rash that is brought on either by contact with a specific chemical to which the patient is uniquely allergic or with a substance that directly irritates the skin. Some chemicals are both irritants and allergens. This rash tends to be weepy and oozy and affects the parts of the skin which have come in direct contact with the offending substance. Common examples of allergic contact dermatitis are poison ivy, poison sumac, poison oak (same chemical, different plant) and reactions to costume jewelry containing nickel.
  4. Stasis dermatitis is a weepy, oozy dermatitis that occurs on the lower legs of individuals who have chronic swelling because of poor circulation in veins.
  5. Psoriasis causes a bumpy scaling eruption which does not weep or ooze. Psoriasis tends to occur on the scalp, elbows, and knees. The skin condition produces silvery flakes of skin that scale and fall off.
  6. Hives (urticaria) are red itchy bumps that come on in a sudden fashion, and then resolve in about eight hours. They tend to recur frequently. If hives are caused by a drug, that drug should be avoided in the future.
  7. Nummular eczema is a weepy, oozy dermatitis that tends to occur as coin-shaped plaques in the wintertime and is associated with very dry skin.
  8. Drug eruptions can occur as certain drugs (like antibiotics) can produce a skin rash as an unwanted side effect. The common appearance is similar to rashes produced by certain common viral infections. On the other hand, drugs may produce a wide variety of other types of rashes.
  9. A heat rash (miliaria) is a skin eruption caused by the occlusion of sweat ducts during hot, humid weather. It can occur at any age but is most common in infants who are kept too warm. Heat rash looks like a red cluster of acne or small blisters. It is more likely to occur on the neck and upper chest, in the groin, under the breasts, and in elbow creases. Treatment involves moving the individual to a cooler environment.

Rashes not caused by infectious organisms, can be treated with over-the-counter 1% hydrocortisone cream for a week or so prior to seeking medical attention. Over-the-counter oral antihistamines like diphenhydramine (Benadryl) or hydroxyzine (Vistaril, Atarax) can be helpful in controlling the itching sensation.

Rashes caused by fungal infections are fairly common. Yeasts are botanically related to fungi and can cause skin rashes. These tend to affect folds of skin (like the skin under the breasts or the groin). They look fiery red and have pustules (blisters) around the edges. Fungus and yeast infections have little to do with hygiene. Fungal rashes are not commonly acquired from dogs or other animals. They seem to be most easily acquired in gyms, showers, pools, or locker rooms, or from other family members.

Rashes produced by bacterial infections: The most common bacterial infections of the skin  are folliculitis and impetigo. Staph or strep germs may cause folliculitis and/or impetigo, two conditions that are much more common in children than adults. Eruptions caused by bacteria are often pustular (the bumps are topped by pus) or may be plaque-like and quite painful (such as with cellulitis).

One of the most common rashes from a parasite infection is scabies. Scabies is produced by a small mite (related to a spider). This mite is usually contracted by prolonged contact with another infected individual. The mite lives in the superficial layers of human skin. It does not produce symptoms until the host becomes allergic to it, which occurs about three weeks after the initial infection. It can resemble eczema. Bedbugs cause a series of eruptions where they pierce the skin.

Rashes that characteristically occur as part of certain viral infections are called exanthems. Many rashes from viruses are more often symmetrical and affect the skin surface all over the body, including roseola and measles. Sometimes certain viral rashes are localized to the cheeks, such as parvovirus infections (fifth disease). Other viral infections, including herpes or shingles, are mostly localized to one part of the body. Patients with such rashes may or may not have other symptoms like coughing, sneezing, localized burning, or stomach upset (nausea). Viral rashes usually last a few days to two weeks and resolve on their own.

Dermatologists, pediatricians, infectious diseases specialists, and many internists are the main specialists who treat rashes. This is a hard task, as they are not easy to diagnose, due to the lack of specificity when talking about a rash. Dermatologists have developed various terms to describe skin rashes. The first requirement is to identify a primary, most frequent feature. The configuration of the rash is then described using adjectives such as ‘circular’, ‘ring-shaped’, ‘linear’, and ‘snake-like’. Other characteristics of the rash that are noted include density, colour, size, consistency, tenderness, shape, and even temperature. Finally, the distribution of the rash on the body can be very useful in diagnosis since many skin diseases have a predilection to appear in certain body areas. Although certain findings may be a very dramatic component of the skin disorder, they may be of limited value in producing an accurate diagnosis. These include findings such as ulcers, scaling, and scabbing. Using this framework, it is often possible to develop a list, called a differential diagnosis, of the possible diseases to be considered. An accurate diagnosis of a skin rash often requires a doctor or other health care professional. On the basis of the differential diagnosis, specific laboratory tests and procedures can be conducted to identify the cause of a particular rash.

Regarding the treatment of rashes, most are not dangerous. Many rashes last a while and get better on their own. It is therefore not unreasonable to treat symptoms like itchy and/or dry skin for a few days to see whether the condition gets milder and goes away.

Over-the-counter treatments include the following:

  • Anti-itch creams containing 1% hydrocortisone cream can be effective
  • Oral antihistamines like diphenhydramine and hydroxyzine can be helpful in controlling the itching.
  • Moisturizing lotions
  • Fungal infections are best treated with topical antifungal medications that contain clotrimazole (Lotrimin), miconazole (Micatin), or terbinafine (Lamisil).

If these measures do not help, or if the rash persists or becomes more widespread, a consultation with a general physician or dermatologist is advisable.

Note that this article is not meant as a tool to self-diagnose, but instead a simple introduction to skin rashes. If you have a rash which is persisting, it is advised that you go to see a dermatologist.

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