What is contact dermatitis?

The term contact dermatitis may not be familiar, but you or your child have experienced it before if you’ve had an allergic reaction to poison ivy or oak. Contact dermatitis involves more of a delayed response, unlike nasal allergies and hives that are mediated by an antibody.

The best examples of allergic contact dermatitis are poison ivy and poison oak. About 70 percent of us are sensitive to the allergen contained in these plants’ oils. The plants like to grow in temperate climates and are native to Africa and North America.  Poison ivy, a climbing plant, is more prevalent on the East Coast. While poison oak, a shrub, seems to be found more in the western part of the United States. It is easy to come in contact with poison ivy or oak while hiking in a wooded area or even weeding your garden. Remember to tell your children this old adage, “Leaves of three, let it be” to avoid exposure to this potentially harmful plant.

Poison ivy can cause symptoms that are quite irritating and stubborn, lasting for a week or two. Contrary to common belief, there is no way to desensitize a person to poison ivy or poison oak, and there is no preventative treatment other than avoidance. The contact allergen in these plants that is responsible for the symptoms is called “Urushiol”.  Other common culprits of allergic contact dermatitis include nickel (found in jewelry, watches, belt buckles), latex, medicines, perfumes and makeup products. In the latter categories, an aromatic substance known as balsam of Peru is often the offending ingredient.

Contact dermatitis usually doesn’t show up immediately. It may take from hours to days for the symptoms to appear in the form of a rash, blisters and weepy lesions. It may last for days or even weeks. In most cases, you just have to tough it out, using topical treatments such as 1 percent hydrocortisone cream to relieve the itching.  In the case of really bad rashes, we may need to prescribe oral steroids especially if there is any danger of infection from open sores, or of the airway being compromised due to swelling around the face and mouth.

Sometimes, patients will present with mysterious rashes that can’t be traced to a particular exposure. We can do a test panel to help pinpoint the source. The patient will leave the patches on for 48 hours, they can’t get them wet, and then we read the results after 72 hours. A typical test panel tests for about 36 different allergens, including natural rubber and nickel.

People who have nasal allergies are no more or less susceptible to contact dermatitis than the rest of the population. Although more common among adults, I have seen cases where a child has had surgery involving a metal implant of some sort that failed because of a possible reaction in the tissue. In these cases, we are often asked to perform a patch test to the implant. Sometimes, though, the presence of a positive patch test to an implant does not necessarily mean that it will cause a reaction when implanted in deep tissue sites. The decision as to whether or not to use a particular implant should therefore be evaluated on a case by case basis, taking into account the potential risks and benefits.

Fun fact: the American Contact Dermatitis Society’s “contact allergen of the year” is methylisothiazolinone (known as MIT). It is a biocide used for controlling microbial growth in water and solutions that contain water. Those most at risk work in the mining, paper manufacturing, metalworking and energy production fields.


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