Allergic Contact Dermatitis
Allergic contact dermatitis is an inflammation resulting from exposure of the skin to a substance to which the individual is allergic. Irritant contact dermatitis, in contrast, is an irritation of the skin caused by a chemical, in which allergy is not a factor. The number and variety of chemicals that can cause allergic contact dermatitis is vast, ranging from the well-known plants of the poison ivy family to obscure chemicals of which the individual may be totally unaware. This problem is distinct from the problem of irritant contact dermatitis, though the rashes may be very similar in appearance.
Only a very small number of individuals are allergic to most chemicals, while as much as 50 percent of the population is allergic to poison ivy. After exposure to some chemicals (e.g. dinitrochlorobenzene), almost everyone will develop an allergy. Infants, children, and old people are generally less susceptible to the development of skin allergies.
After the allergenic substance comes in contact with the skin, the rash usually develops one or two days later. If the individual has never before been exposed to the chemical or to a similar substance, it will take a week or more for him to become allergic to it and develop a rash. This is called the latent or incubation period.
Once an allergy of this type is established it tends to persist for many years. If one area of the skin, no matter how small, becomes allergic to a substance, the skin of the entire body will also be allergic to it.
Exposure to the offending chemical or plant may be brief and casual, but all that is required for a rash to develop is that some of the chemical penetrate the superficial layers of the skin. (This takes only about ten minutes in the case of poison ivy oils.) Many people with allergic contact dermatitis have no idea what caused their rash, because of the brevity of exposure and the delay in the development of the rash. Frequently, they fail to notice or identify the substance at the time of exposure.
In milder cases of allergic contact dermatitis, the rash may consist only of redness, bumps, and mild to moderate itching. Severe cases develop swelling, blisters, oozing and crusts, and severe itching. The rash often appears as a haphazard distribution of streaks and patches, especially with plant allergies. In later stages of the rash, the skin becomes thickened, dry, and scaly; cracking and chapping may occur. The rash of allergic contact dermatitis usually lasts about ten to fifteen days, but may last longer if the dermatitis is severe or secondary infection develops.
A common fallacy is that the rash "spreads" via" the fluid that drains from the blisters. Other areas may develop the dermatitis over a period of several days, but this is caused by varying amounts of the chemical on skin sites that have different degrees of sensitivity. For example, bits of the plant or its sap under the nails can spread the rash. The skin around the eyes and the skin of the neck, groin, and genitalia is the most sensitive, while the scalp, palms, and soles are the most resistant to contact dermatitis, whether irritant or allergic.
Only a very small number of individuals are allergic to most chemicals, while as much as 50 percent of the population is allergic to poison ivy. After exposure to some chemicals (e.g. dinitrochlorobenzene), almost everyone will develop an allergy. Infants, children, and old people are generally less susceptible to the development of skin allergies.
After the allergenic substance comes in contact with the skin, the rash usually develops one or two days later. If the individual has never before been exposed to the chemical or to a similar substance, it will take a week or more for him to become allergic to it and develop a rash. This is called the latent or incubation period.
Once an allergy of this type is established it tends to persist for many years. If one area of the skin, no matter how small, becomes allergic to a substance, the skin of the entire body will also be allergic to it.
Exposure to the offending chemical or plant may be brief and casual, but all that is required for a rash to develop is that some of the chemical penetrate the superficial layers of the skin. (This takes only about ten minutes in the case of poison ivy oils.) Many people with allergic contact dermatitis have no idea what caused their rash, because of the brevity of exposure and the delay in the development of the rash. Frequently, they fail to notice or identify the substance at the time of exposure.
In milder cases of allergic contact dermatitis, the rash may consist only of redness, bumps, and mild to moderate itching. Severe cases develop swelling, blisters, oozing and crusts, and severe itching. The rash often appears as a haphazard distribution of streaks and patches, especially with plant allergies. In later stages of the rash, the skin becomes thickened, dry, and scaly; cracking and chapping may occur. The rash of allergic contact dermatitis usually lasts about ten to fifteen days, but may last longer if the dermatitis is severe or secondary infection develops.
A common fallacy is that the rash "spreads" via" the fluid that drains from the blisters. Other areas may develop the dermatitis over a period of several days, but this is caused by varying amounts of the chemical on skin sites that have different degrees of sensitivity. For example, bits of the plant or its sap under the nails can spread the rash. The skin around the eyes and the skin of the neck, groin, and genitalia is the most sensitive, while the scalp, palms, and soles are the most resistant to contact dermatitis, whether irritant or allergic.
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