Eczema is not really a single disease of the skin. Rather, "eczema" is a generic name for a particular kind of skin reaction where you see itching, fluid weeping or oozing from the rash, and lichenification (skin thickening where the normal fine lines on the skin surface become deeper and stand out more).
Like other diseases, eczema can be acute (happening relatively suddenly) or chronic (happening for a long time). Acute eczema usually comes with redness, oozing and weeping, and microscopic "vesicles" or fluid-filled pockets in the epidermis (the outermost layer of skin). Chronic eczematous skin is usually thickened, scaly, and dried; the skin colour may change (lighter or darker), and lichenification may be more severe. Eczema is often an allergic reaction to something that contacts the skin, and people with eczema also tend to have allergic rhinitis, asthma, or both.
The term "eczema" is generic: there are several different varieties, with different causes, different appearance, and sometimes different treatments.
As the name suggests, contact dermatitis is caused by noxious things coming in contact with the skin. The skin injury may be irritant (resulting from direct chemical or mechanical damage to the skin) or allergic (caused by an allergic reaction to something that contacts the skin). The two kinds are not entirely separate -- the main difference is that allergic reactions occur mainly in those people who have become allergic to the substance they touch, while irritants are irritating to just about everyone who touches them. That's not much of a difference: the oils produced by poison ivy, poison oak, and poison sumac are technically allergens, but you become sensitive to them so quickly that they might as well be irritants.
Irritant-based contact dermatitis is more common than allergic-based, especially in children. Lots of things can irritate the skin, including:
Atopic dermatitis, practically speaking, is a dermatitis whose
cause is not known. Often it appears along with contact dermatitis,
but persists long after you've eliminated every possible allergen and
irritant. Often atopic dermatitis appears as unusually dry skin.
Mild atopic dermatitis and contact dermatitis
can be aggravated by anything that dries out
the skin -- including cold weather, and soap and water. And, although
atopic dermatitis can appear without other allergy problems, it often
shows up in children who later develop
Treating Atopic and Contact Dermatitis
Mild cases of atopic dermatitis can often be treated with just a good moisturizing hand or body lotion. The "greasier" lotions often work better: washing with soap and water removes dirt from your skin, but also removes the natural oils from your skin and makes it drier. Some people are so sensitive to dry skin that they must apply lotion to their entire body right after each bath or shower, before the water left on their skin dries out (water actually dries skin out very quickly as it evaporates; that's why you need to replenish the oils as well). Compulsive hand-washers -- including doctors, nurses, and other health-care workers -- often have dry-skin problems that approach that of people with atopic dermatitis. My own hands often crack and sometimes bleed by the end of a day in the office or hosiptal, which isn't surprising since I may have to wash my hands 50-100 times on a busy day; I usually apply a good, greasy hand lotion (such as Eucerin®), or both an ordinary hand lotion and Vaseline®, to my hands at bedtime just to replenish all the natural oils I've washed out of my hands during the day.
For more severe atopic dermatitis, we sometimes have to resort to steroid treatment. Usually we start with mild "topical" (applied to the skin) steroid creams or lotions -- so mild that they can be bought over-the-counter without a prescription -- and in many cases that's all that is needed. (I do suggest to my patients, and to you, that you not use even over-the-counter steroids without talking to your doctor first. Even the over-the-counter steroids can be hazardous, especially if you don't use them properly.) If the OTC steroids don't work, we may then suggest more potent topical steroids, which do have to be prescribed by your doctor. Sometimes -- very rarely -- a patient may need oral steroids; I usually send patients of mine who need oral or the very strong topical steroids to a dermatologist. One possible side effect of using topical steroids for a long time, especially on the face, is atrophy of skin tissue; therefore, we try to avoid long-term topical steroids whenever we can, using them only for bad flare-ups.
Really bad atopic dermatitis may not respond very well to steroids. Some of these patients respond to tacrolimus, a medicine originally developed to treat certain kinds of cancer, or pimecrolimus, which is similar to tacrolimus but was intended mainly for treatment of severe eczema. Like all cancer drugs, tacrolimus and pimecrolimus have potential side effects, and we do not prescribe these medications unless everything else fails.
Contact dermatitis can sometimes be treated with the same strategies we use for atopic dermatitis. First, though, you need to identify the irritant or allergen and get it away from you -- it's always better to remove the cause of a rash than to use medicines to get rid of the rash. In most cases removing the irritant is all the treatment you need.