Irritant Contact Dermatitis
Irritant contact dermatitis occurs as a result of exposure to chemicals. providing skin comes into contact with sufficient concentration of a irritant chemical for enough time, dermatitis will result. Irritant contact dermatitis is indescriminate in as much similarly exposed individuals will exhibit similar symptoms. There is no immunological and therefore no allergic component to the disease.
Where certain individuals do appear more susceptible to this kind of dermatitis it is due to other factors that compromise the skin's natural barrier of protection. For example, constant exposure to water can reduce the skin's ability to withstand chemical attack. Cuts and scratches can allow entry of chemicals through the protective outer layers of the skin into the more sensitive dermis k layer.
Allergic Contact Dermatitis
Allergic contact dermatitis only affects individuals who are 'sensitised'. Typically the patient will have been exposed to the chemical for a period of time without symptoms occurring. During this latent period sensitisation may develop. The occurrence of symptoms indicates that an allergy has developed. Typically the patient will now develop symptoms following exposures which do not cause symptoms in 'normal' subjects.
The process by which sensitisation develops is not clear cut. Sometimes sensitisation may occur after a single high exposure whereas in other cases it may take years to develop. It is worth reiterating that allergic contact dermatitis occurs in sensitised patients at chemical concentrations too low to cause symptoms in normal, unsensitised controls.
Diagnosis of sensitisation is fairly straightforward. A patient is subjected to either 'patch' or 'scratch' testing with the suspect substance. This is usually done on skin that is not normally exposed such as the arm or the back. Several substances may be tested and ideally the patient should be 'blind' to what each substance is. A positive reaction is scored relative to accepted standards. Sometimes to confirm an allergic response the test is also performed on a volunteer control.
preventing dermatitis is considerably more preferable than treatment. For both irritant and contact dermatitis the key is as far as possible to avoid exposure to hazardous chemicals. Where exposure is unavoidable, handling should be of minimal duration and handling with a compromised skin barrier (due to cuts, cracks or scratches) should be avoided altogether.
It is important to note that combinations of chemicals, and chemicals in combination with wet hands may pose a greater hazard than exposure to a chemical in isolation. Consequently the prevention of dermatitis is often achieved by the design of safer work practices.
Glossary of Terms
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