There are two types of dermatitis caused by substances coming in contact with the skin:
- Irritant dermatitis
- Allergic contact dermatitis.
Irritant dermatitis is an inflammatory reaction in the skin, resulting from exposure to a substance that causes an eruption. Allergic contact dermatitis is an acquired sensitivity to various sub-stances that produce inflammatory reactions in those, and only those, who have been previously sensitized to the allergen.
Irritant contact dermatitis
Many substances act as irritants that produce a nonspecific inflammatory reaction of the skin. This type of dermatitis may be induced in any person if a sufficiently high concentration is used. No previous exposure is necessary and the effect is evident within minutes, or a few hours at most. The concentration and type of the toxic agent, the duration of exposure, and the condition of the skin at the time of exposure produces the variation in the severity of the dermatitis from person to person, or from time to time in the same person.
The skin may be more vulnerable by reason of maceration from excessive humidity, or exposure to water, heat, cold, pressure, or friction. Dry skin is less likely to react to contactants. Thick skin is less reactive than thin. Repeated exposure to some of the milder irritants may, in time, produce a hardening effect. This process makes the skin more resistant to the irritant effects of a given substance. Symptomatically, pain and burning are more common in irritant dermatitis, contrasting with the usual itch of allergic reactions.
Irritant dermatitis is often produced by alkalis such as soaps, detergents, bleaches, ammonia preparations, lye, drain pipe cleaners, and toilet bowl and oven cleansers. Alkalis penetrate and destroy deeply because they dissolve keratin. Strong solutions are corrosive and immediate application of a weak acid
such as vinegar, lemon juice, or 0.5% hydrochloric acid solution will lessen their effects. The principal compounds are sodium, potassium, ammonium, and calcium hydroxides.
The powerful acids are corrosive, whereas the weaker ones are astringent. Hydrochloric acid produces burns that are less deep and more liable to form blisters than injuries from sulfuric and nitric acids. Hydrochloric acid burns are encountered in those who handle or transport the product, and in plumbersand those who work in galvanizing or tin-plate factories.
Airbags are deployed as a safety feature on cars when rapid deceleration occurs. Activation of a sodium azide and cupric oxide propellant cartridge releases nitrogen gas, which expands at speeds exceeding 160 km/h. Talcum powder, sodium hydroxide, and sodium carbonate are released into the bag. Abrasions, thermal, friction, and chemical burns, and an irritant contact dermatitis may result. Superficial erythema may respond well to topical steroids, but full-thickness burns may occur and require debridement and grafting
Some metal salts that act as irritants are the cyanides of calcium, copper, mercury, nickel, silver, and zinc, and the chlorides of calcium and zinc. Bromine, chlorine, fluorine, and iodine are also irritants. Occupational exposure to methyl
bromide may produce erythema and vesicles in the axillary and inguinal areas. Insecticides, including 2,2-dichlorovinyl dimethyl phosphate used in roach powder and fly repellents and killers, can act as irritants.
Allergic contact dermatitis
Allergic contact dermatitis results when an allergen comes into contact with Previously sensitized skin. It is due to a specific acquired hypersensitivity of the delayed type, also known as cell-mediated hypersensitivity or immunity. Occasionally, dermatitis may be induced when the allergen is taken internally by a patient first sensitized by topical application; this occurs, for example, with substances such as cinnamon oil or various medications. The anamnestic response is termed systemic contact dermatitis. It may appear first at the site of the prior sensitization or past positive patch test, but may spread to a generalized morbilliform or eczematous eruption.
The most common causes of contact dermatitis in the US are: toxicodendrons (poison ivy, oak, or sumac), nickel, balsam of Peru (Myroxylon pereirae), neomycin, fragrance, thimerosal, gold, formaldehyde and the formaldehyde releasing preservatives, bacitracin, and rubber compounds. Frequent positive reactions to thimerosal do not often correlate with clinical exposure histories.
In some instances, impetigo, pustular folliculitis, and irritations or allergic reactions from applied medications are super-imposed on the original dermatitis.
A particularly vexing situation is when allergy to topical steroids complicates an eczema, in which case the preexisting dermatitis usually does not flare, but simply does not heal as expected. The cutaneous reaction may also provoke a hypersusceptibility to various other previously innocuous substances, which continues the eczematous inflammatory response indefinitely.
These eruptions resolve when the cause is identified and avoided.
For acute generalized allergic contact dermatitis treatment with systemic steroidal agents is effective, beginning with 40–60 mg/day prednisone in a single oral dose, and tapering slowly to topical steroids. When the eruption is limited in extent and severity, local application of topical corticosteroid creams, lotions, or aerosol sprays is preferred.
Testing for sensitivity
The patch test is used to detect hypersensitivity to a substance that is in contact with the skin so that the allergen may be determined and corrective measures taken. So many allergens can cause allergic contact dermatitis that it is impossible to test a person for all of them. In addition, a good history and observation of the pattern of the dermatitis, its localization on the body, and its state of activity are all helpful in determining the cause.
The patch test is confirmatory and diagnostic, but only within the framework of the history and physical findings; it is rarely helpful if it must stand alone. Interpretation of the
relevance of positive tests and the subsequent education of patients are challenging in some cases.
The Contact Allergen Avoidance Database (CARD) provides names of alternative products that may be used by patients when an allergen is identified. This is available through the American Contact Dermatitis Society.
Occupational contact dermatitis
Workers in various occupations are prone to contact dermatitis from primary irritants and allergic contactants. In certain occupations it is a common occurrence. It is more frequent in the workplace, but it is less severe and less chronic than allergic contact dermatitis.
Occupational skin disease has declined over the past 30 years but still constitutes approximately 10% of all occupational disease cases. Agriculture, forestry, and fishing have the highest incidence of occupational skin disease, with the manufacturing and healthcare sectors contributing many cases as well.
Irritant contact dermatitis is commonly present in wet-work jobs, and allergy occurs in hairdressers, machinists, and many others with unique exposures to multiple sensitizing chemicals. The hands are the parts most affected, being involved in 60% of allergic reactions and 80% of irritant dermatitis. Epoxy resin is an allergen that appears more frequently when evaluating occupational patients. The allergens most frequently encountered in occupational cases are carba mix, thiuram mix, epoxy resin, formaldehyde, and nickel.
The first measure in the management of occupational contact dermatitis is to eliminate skin contact with the irritating and sensitizing substances.
The work environment should be controlled, with use of all available protective devices to prevent accidental exposures. Personal protective measures, such as frequent clothing changes, cleansing showers, protective clothing, and protective barrier creams.