What is dermatitis?

Causes and Symptoms

The term
dermatitis
refers not to a single skin
disease but to a wide range of disorders. Dermatitis is often used interchangeably with
eczema
. The two most common dermatitides are atopic (allergic) dermatitis, in which the individual appears to inherit a predilection for the disease, and contact dermatitis, in which the individual’s skin reacts immediately on contact with a substance or develops sensitivity to it.

Atopic dermatitis often occurs in individuals with a personal or family history of allergy, such as hay fever or
asthma. Between 50 and 70 percent of children with severe atopic dermatitis develop asthma, a rate that is more than five times higher than for the general population. These people often have high serum levels of a certain antibody, immunoglobulin E (IgE), which may be associated with their skin’s tendency to break out, although a specific antigen-antibody reaction has not been demonstrated.

There are many distinct characteristics of atopic dermatitis, some of which depend on the age of the patient. The disease usually starts early in childhood. It is often first discovered in infants in the first months of life when redness and weeping, crusted lesions appear mostly on the face, although the scalp, arms, and legs may also be affected. There is intense itching. Papules (pimples), vesicles (small, blisterlike lesions filled with fluid), edema (swelling), serous exudation (discharge of fluid), and scaly crusts may be seen. At one year of age, oval, scaly lesions appear on the arms, legs, face, and torso. In older children and adults, the lesions are usually localized in the crook of the elbow and the back of the knees, and the face and neck may be involved. The course of the disease is variable. It usually subsides by the third or fourth year of life, but periodic outbreaks may occur throughout childhood, adolescence, and adulthood. Cases persisting past the patient’s middle twenties, or beginning then, are the most difficult to treat.

Dryness and itching are always present in atopic dermatitis. People with atopic dermatitis seem to lose skin moisture more readily than average people: Rather than soft, pliable skin, they develop dry, rough, sensitive skin that is particularly prone to chapping and splitting. The skin becomes itchy, and the individual’s tendency to scratch significantly aggravates the condition in what is called the “itch-scratch-itch” cycle or the “scratch-rash-itch” cycle: the individual scratches to relieve the itching, which causes a rash, which in turn causes increased itching, which invites increased scratching and increased irritation. After years of itching and scratching, the skin of older children and adults with atopic dermatitis develops red, lichenified (rough, thickened) patches in the crook of the arm and behind the knees as well as on the eyelids, neck, and wrists.

Constant chafing of the affected area invites bacterial infection and lymphadenitis (inflammation of lymph nodes). Furthermore, patients with atopic dermatitis seem to have altered immune systems. They appear to be more susceptible than others to skin infections, warts, and contagious skin diseases. Staphylococcus aureus and certain streptococci are common infecting bacteria in these patients. Pyoderma is often seen as a result of bacterial infection in atopic dermatitis. This condition features redness, oozing, scaling, and crusting as well as the formation of small pustules (pus-filled pimples).

Patients with atopic dermatitis are also particularly sensitive to
herpes simplex and vaccinia viruses. Exposure to either could cause a severe skin disease called Kaposi’s varicelliform eruption. Vaccinia virus (the agent that causes cowpox) is used in the preparation of
smallpox vaccine. Therefore, patients with atopic dermatitis must not be vaccinated against smallpox. Furthermore, they must be isolated from patients with active herpes simplex and those recently vaccinated against smallpox.

Patients with atopic dermatitis may also develop contact dermatitis, which can greatly exacerbate their condition. They are also sensitive to a wide range of allergens, which can bring on outbreaks, as well as to low humidity (such as in centrally heated houses in winter), which can contribute to dry skin. They may not be able to tolerate woolen clothing.

A condition called keratosis pilaris often develops in the presence of atopic dermatitis. It is not seen in young infants, but it does appear in childhood. Hair follicles on the torso, buttocks, arms, and legs become plugged with horny matter and protrude above the skin, giving the appearance of goose bumps or “chicken skin.” The palms of the hands of patients with atopic dermatitis have significantly more fine lines than those of average people. In many patients, there is a tiny “pleat” under the eyes. They are often prone to cold hands and may have pallor, seen as a blanching of the skin around the nose, mouth, and ears.

When ordinary skin is lightly rubbed with a pointed object, almost immediately there is a red line, followed by a red flare, and finally, a wheal or slight elevation of the skin along the line. In patients with atopic dermatitis, however, there is a completely different reaction: The red line appears, but almost instantly it becomes white. The flare and the wheal do not appear.

About 4 to 12 percent of patients with atopic dermatitis develop
cataracts at an early age (some estimates range as high as nearly 40 percent). Normally, cataracts do not appear until the fifties and sixties; those with atopic dermatitis may develop them in their twenties. These cataracts usually affect both eyes simultaneously and develop quickly.

Psychologically, children with atopic dermatitis often show distinct personality characteristics. They are reported to be bright, aggressive, energetic, and prone to fits of anger. Children with severe, unmanageable cases of atopic dermatitis may become selfish and domineering, and some go on to develop significant personality disorders.

It is not known exactly what happens to cause the itching and dry skin that are the fundamental signs of atopic dermatitis and the root of many of its complications. Theories suggest various origins. It is by definition an allergic disorder, but the allergens that are specifically involved and how they produce the signs of atopic dermatitis are unknown. One of the most interesting theories involves the antibody IgE. Theoretically, the union of IgE with an antigen causes certain cells to release pharmacologic mediators, such as histamine, bradykinin, and slow-reacting substance (SRS-A), that cause itching and thus begin the cycle of scratching and irritation characteristic of atopic dermatitis. The fact that patients with atopic dermatitis have higher than normal levels of IgE, and that there is a relationship between IgE levels and the severity of atopic dermatitis, seems to lend support to this theory.

Contact dermatitis resembles atopic dermatitis at certain stages, but the dry skin of atopic dermatitis may not be seen. Contact dermatitis is usually characterized by a rash consisting of small bumps, itchiness, blisters, and general swelling. It occurs when the skin has been exposed to a substance to which the body is sensitive or allergic. If the contact dermatitis is caused by direct irritation by a caustic substance, it is called irritant contact dermatitis. The causative agents are primary irritants that cause inflammation at first contact. Some obvious irritants are acids, alkalis, and other harsh chemicals or substances. An example is fiberglass dermatitis, in which fine glass particles from fiberglass fabrics or insulation enter the skin and cause redness and inflammation.

If the dermatitis is caused by allergic
sensitivity to a substance, it is called allergic contact dermatitis. In this case, it may take hours, days, weeks, or years for the patient to develop sensitivity to the point where exposure to these substances causes allergic contact dermatitis. Agents that may cause allergic contact dermatitis include soaps, acetone, skin creams, cosmetics, poison ivy, and poison sumac.

Allergic contact dermatitis comprises the largest variety of contact dermatitides, many of them named for the allergens that cause them. Hence, there is pollen dermatitis; plant and flower dermatitis, such as poison ivy or poison oak; clothing dermatitis; shoe, and even sandal strap, dermatitis; metal and metal salt dermatitis; cosmetic dermatitis; and adhesive tape dermatitis, among others. They all have one thing in common: the skin is exposed to an allergen from any of these sources and becomes so sensitive to it that further exposure causes a rash, itching, and blistering.

The development of sensitivity to an allergen is an immunological response to exposure to that substance. With many allergens, the first contact elicits no immediate immunological reaction. Sensitivity develops after the allergen has been presented to the T lymphocytes that mediate the immune response.

Because it often takes a long time to develop sensitivity, patients are surprised to discover that they have become allergic to substances that they have been using for years. For example, a patient who has been applying a topical medication to treat a skin condition may one day find that the medication causes an outbreak of dermatitis. Ironically, some of the ingredients in medications commonly used to treat skin conditions are among the major allergens that cause allergic contact dermatitis. These include antibiotics, antihistamines, topical anesthetics, and antiseptics as well as the inactive ingredients used in formulating the medications, such as stabilizers.

Other substances to which the patient may develop sensitivity include the chemicals used in making fabric for clothing, tanning chemicals used in making leather, dyes, and ingredients in cosmetics. Many patients develop sensitivity to allergens found in the workplace. The list of potential allergens in the industrial setting is virtually endless and includes solvents, petroleum products, chemicals commonly used in manufacturing processes, and coal tar derivatives.

In some cases, the allergen requires sunlight or other forms of light to precipitate an outbreak of contact dermatitis. This is called photoallergic contact dermatitis, and it may be caused by such agents as aftershave lotions, sunscreens, topical sulfonamides, and other preparations applied to the skin. Another light reaction, termed phototoxic contact dermatitis, can be caused by exposure to sunlight after exposure to perfumes, coal tar, certain medications, and various chemicals.

A different form of dermatitis involves the sebaceous glands, which secrete sebum, a fatty substance that lubricates the skin and helps retain moisture. Sebaceous dermatitis is usually seen in areas of the body with high concentrations of sebaceous glands, such as on the scalp or face, behind the ears, on the chest, and in areas where skin rubs against skin, such as the buttocks and the groin. It is seen most often in infants and adolescents, although it may persist into adulthood or start at that time.

In infants, sebaceous dermatitis can begin within the first month of life and appears as a thick, yellow, crusted lesion on the scalp called cradle cap. There can be yellow scaling behind the ears and red pimples on the face. Diaper rash may be persistent in these infants. In older children, the lesion may appear as thick, yellow plaques in the scalp. When sebaceous dermatitis begins in adulthood, it starts slowly, and usually its only manifestation is scaling on the scalp (dandruff). In severe cases, yellowish-red scaling pimples develop along the hairline and on the face and chest. Its cause is unknown, but a yeast commonly found in the hair follicles, Pityrosporum ovale, may be involved.

There are many other kinds of dermatitis. Diaper dermatitis, or diaper rash, is a complex skin disorder that involves irritation of the skin by urine and feces, irritation by constant rubbing, and secondary infection by Candida albicans. Nummular dermatitis is characterized by crusting, scaly, disc-shaped papules and vesicles filled with fluid and often pus. Pityriasis alba is a common dermatitis with pale, scaly patches. In lichen simplex chronicus, there is intense itching, with lesions caused and perpetuated by scratching and rubbing. Stasis dermatitis occurs at the ankles; brown discoloration, swelling, scaling, and varicose veins are common. Hyperimmunoglobulin E (Hyper IgE) syndrome is characterized by extremely high IgE levels, ten to one hundred times higher than normal, and a family history of allergy; the patient has frequent skin infections, suppurative (pus-forming) lymphadenitis, pustules, plaques, and abscesses. Pompholyx occurs on the hands and soles of the feet; there is excessive sweating, with eruptions of deep vesicles accompanied by burning or itching.

Friction can also cause dermatitis. In intertrigo, the friction of skin rubbing against skin causes inflammation that can become infected. In frictional lichenoid dermatitis, or sandbox dermatitis, it is thought that the abrasive action of sand or other gritty material on the skin causes the characteristic lesions. Winter
eczema seems to be caused by the skin-drying effects of low humidity as well as by harsh soaps and overfrequent bathing; dry skin and itching are common. The acrodermatitis diseases may be limited to the hands and feet, or, like acrodermatitis enteropathica, may erupt in other parts of the body, such as around the mouth and on the buttocks. In fixed-drug eruption, lesions appear in direct response to the administration of a drug; the lesions are generally in the same parts of the body, but they may spread. Swimmer’s itch is a parasitic infection from an organism that lives in freshwater lakes and ponds, while seabather’s eruption seems to be caused by a similar saltwater organism.

Treatment and Therapy

Many dermatitides resemble one another, and it is important for a physician to identify the patient’s complaint precisely to treat it effectively. Therefore, the physician will confirm the identity of the condition through a process known as differential diagnosis. This method allows him or her to rule out all similar conditions, pinpoint the exact nature of the patient’s problem, and develop a therapeutic regimen to treat it.

In treating atopic dermatitis, one of the first goals is to relieve dryness and itching. The patient is cautioned not to bathe excessively, as this dries the skin. Lotions are used to lubricate the skin and retain moisture. The patient is advised not to scratch, because this could break the skin and invite infection. The patient is also advised to avoid any known offending agents and cautioned not to apply any medication to the skin without the doctor’s knowledge.

Wet compresses can bring relief to patients with atopic dermatitis. Topical
corticosteroids are used to help resolve acute flare-ups, but only for short-term therapy, because their prolonged use might produce undesirable side effects. Oral
antihistamines are often given to relieve itching and to help the patient sleep. Diet may play a role in atopic dermatitis in infants; some pediatric dermatologists and other physicians recommend elimination of milk, eggs, tomatoes, citrus fruits, wheat products, chocolate, spices, fish, and nuts from the diets of these patients. Soft cotton clothing is recommended, as is the avoidance of pets or fuzzy toys that might be allergenic. For secondary infections that arise from atopic dermatitis, the physician prescribes appropriate antibiotic therapy.

In primary irritant contact dermatitis, the offending agent is eliminated or avoided. In allergic contact dermatitis, one of the main goals is to discover the offending agent so that the patient can avoid contact with it. Sometimes this information can be elicited from the patient interview, and sometimes it is necessary to conduct a series of patch tests. In this procedure, known allergens are applied to the skin of the patient to find those that cause irritation. Avoidance of the offending agent can cause the patient some difficulty if the agent happens to be something that is found everywhere. An example is the metal nickel, which is in coins, jewelry, and hundreds of other objects. Patients who insist on wearing jewelry containing nickel are advised to paint it with clear nail polish periodically to avoid contact of the metal with the skin. Similarly, many other allergens are in common use. Patients are advised to read cosmetics labels and food and medical ingredients lists to avoid contact with agents to which they are sensitive.

Because there is such a wide range of allergic contact dermatitides, treatments vary considerably. Topical and oral
steroids are used, as well as antihistamines. Sometimes the physician finds it necessary to drain large blisters and apply drying agents to weeping lesions. Sometimes the condition calls for wet compresses to relieve itching and soothe the patient. Specialized lotions, soaps, and shampoos are also used, some to treat dryness and others, as in the case of sebaceous dermatitis, to remove scales and to relieve oiliness.

Other treatments depend on the type of dermatitis from which the patient suffers. Patients with photoallergic or phototoxic dermatitis are advised to avoid light. Acrodermatitis enteropathica is caused by a zinc deficiency; in addition to palliative therapy to relieve the symptoms, these patients are given zinc sulfate, which results in complete remission of the disease. As with atopic dermatitis, bacterial infections occurring as a result of a flare-up of allergic contact dermatitis are treated with appropriate antibiotic therapy.

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