People are often given a diagnosis of 'contact dermatitis', but what exactly is that? What are the implications
| "True contact allergic dermatitis is caused by particular substances" |
Now, more importantly, what are the types and causes of contact dermatitis? The condition is broadly divided into two categories, irritant and allergic. So we speak of contact irritant dermatitis and contact allergic dermatitis. Why is this important? Because it tells us about the possible causes and ways to avoid the condition.
Basically, contact irritant dermatitis is caused by chemicals or substances that will irritate skin in any person. An example would be a retinoid drug, such as Retin A. While the drug is very useful for many reasons, if used too much or too quickly, it will cause irritation in almost any individual. So a person may think 'I'm allergic to Retin A' when in reality there is no allergy but just irritation which can be overcome. So what is 'allergic' dermatitis?'
True contact allergic dermatitis is caused by particular substances that cause a person to launch an immune reaction to the substance. An example would be the topical antibiotic neomycin. Many people would typically apply this drug to various cuts, scrapes or injuries, thinking they will prevent an infection. Often, however, days or weeks later they will develop itching and rash at the site, and have become truly allergic to the drug neomycin. In fact, neomycin is one of the most common topical sensitizing drugs in North America. A typical comment by the patient might be 'but I've used this many times before!' and that is just the point. Allergic dermatitis can not occur unless the skin had been exposed prior, it was over several applications that the allergy was being created!
So there you have it, two different types of contact dermatitis that can look exactly the same, but with entirely different causes!
Joel Lamm, M.D.