Most people are familiar with the poison ivy rash. Chances are that you or someone you know unknowingly came in contact with this plant and later developed a red, irritated, itchy memento. The poison ivy rash is perhaps the best known example of contact dermatitis. Contact dermatitis refers to inflammation of the skin, occurring after exposure to certain substances. There are two main types of contact dermatitis: irritant contact dermatitis and allergic contact dermatitis. Irritant contact dermatitis is more common, comprising 80% of cases.
Who gets it?
To get contact dermatitis, you first need to be exposed to an irritating substance for the time required to incite a reaction. For allergic contact dermatitis, you also need the individual immune characteristics necessary for a reaction to occur. Those most at risk for occupational irritant contact dermatitis include housekeepers, hairdressers, and medical/dental/veterinary professionals.
What causes it?
The list of causative agents is quite extensive and includes plants, cosmetics, topical medications, jewelry, cleaning supplies, metal belts, underwear elastic, sunscreen ingredients, soap, and shoe materials.
In the case of irritant contact dermatitis, some substances to watch out for include soaps, detergents, excessive water, industrial solvents (e.g. petroleum, acetone, ethylene glycol ether), and plants (e.g. capsaicin, pepper, prickly pear).
In the case of allergic contact dermatitis, the North American Contact Dermatitis Group has composed a list of Top 10 contact allergens: nickel, gold, Balsam of Peru, thiomerosal, neomycin sulfate, fragrance mix, formaldehyde, cobalt chloride, bacitracin, and quaternium 15. More details can be found here.
Why does it occur?
One of the main differences between irritant and allergic contact dermatitis is how the dermatitis arises. In irritant contact dermatitis, substances have direct toxic effects on the skin. In allergic contact dermatitis, substances trigger an immunologic reaction, one manifestation of which is irritated skin.
Irritant contact dermatitis can occur in everyone because it is dependent on the extent of exposure to a substance. Many people develop irritant contact dermatitis via cumulative exposure to certain chemicals (this often occurs in the work environment), while others develop irritant contact dermatitis after just one encounter (usually due to very strong irritants). Irritant contact dermatitis usually appears within hours of exposure – the harsher the substance, the faster a reaction develops.
In contrast, allergic contact dermatitis only occurs in certain people. It is caused by allergens and is similar to other types of allergies. In the same way that someone with a pollen allergy will develop a runny nose and runny eyes when exposed to pollen, someone whose immune system has become sensitized to poison ivy will develop an irritated skin reaction when exposed to poison ivy. It is important to note that a person must become sensitized to the substance in question before it can result in a rash. Some people become sensitized after just one exposure, while others may abruptly become sensitized after years of exposure without consequence. Once sensitization occurs, the immune system will mount a specific response upon re-exposure to that substance, and this response will manifest itself as irritated skin. Allergic contact dermatitis usually appears 1-2 days after exposure, although it can occur anywhere from 8 hours to 7 days after exposure.
Photoallergic contact dermatitis only manifests itself when allergen-contacted skin is also exposed to sunlight. In this scenario, reactions occur only in sun-exposed areas of the skin. This rash often looks like sunburn but occurs independent of excessive sun exposure.
Signs & symptoms
Contact dermatitis can be very itchy. It is often characterized by a burning, stinging sensation. In addition, some people with severe allergic contact dermatitis can feel feverish.
In terms of appearance, contact dermatitis presents on a spectrum, depending on how acute (recently-acquired) or chronic (long-standing) it is. The rash can be red, swollen, blistering, weeping, oozing, crusting, and scaling. It usually contains tiny blisters that look like pimples, the difference being that the fluid is clear as opposed to pus-like. Of note, this rash usually has very clearly-defined boundaries.
Although irritant contact dermatitis is confined to the areas the causative substance came in contact with, allergic contact dermatitis is not confined to the areas of exposure. In fact, it can spread to distant areas of the body. One thing to know about allergic contact dermatitis is that it often becomes worse with repeated exposures.
While acute chronic dermatitis tends to be angry, red and marked by vesicles or blisters, chronic contact dermatitis is marked by lichenification (thickened, leathery skin that is usually caused by scratching), and dry, chapped skin with fissures and crusts.
Often, where the rash occurs can give you and your dermatologist a clue as to what may have caused it. Some allergens cause distinct patterns of reaction. For example, poison ivy will present as a line of papules and vesicles.
Other allergens confine their reactions to the sites of immediate contact. For example, if the causative allergen is located in your shoes, the dermatitis may be limited to your foot. Similarly, a glove distribution is useful in identifying an allergic ingredient in your gloves. If the rash is limited to your lips, it may be caused by lipstick or lip gloss. Dermatitis caused by jewelry can acquire the distinctive shape of the ring, necklace, or bracelet that caused it. If dermatitis is on the scalp, it may be due to a shampoo, dye, or other hair product. If the dermatitis is just on the eyelids, it may have been caused by a cosmetic or spread by an allergen originally on the hands. Of note, irritant contact dermatitis is most likely to occur on the hands.
Diagnosis
With both irritant and allergic contact dermatitis, the story of how your rash developed and what substances you have been exposed to will be very important to your dermatologist. Before your visit, you should think about what substances you were exposed to before the dermatitis began. What do you regularly handle at work? Have you recently encountered one of the agents listed above? Have you just tried a new product? Prior to your visit, you can attempt your own elimination trial by removing a suspected agent and observing whether the dermatitis clears.
Sometimes, fungal cultures may need to be taken to exclude other etiologies. Biopsies may also help exclude other causes but are not a definitive way to diagnose contact dermatitis.
Based on your story, elimination trials can be used to identify possible causative agents. If eliminations trials do not identify the causative agent and the rash persists, patch testing may be utilized. Although it does not work for irritant contact dermatitis (as there is no allergic reaction involved), patch testing can be quite useful in the case of allergic contact dermatitis.
Once contact dermatitis is diagnosed, how can it be treated?
REFERENCES:
Contact Dermatitis [Internet]. Mayo Clinic. http://www.mayoclinic.com/health/contact-dermatitis/DS00985. Accessed on March 2nd, 2010.
Hogan, DJ. Allergic Contact Dermatitis [Internet]. eMedicine. http://emedicine.medscape.com/article/1049216-overview. Accessed on March 2nd, 2010.
Marks JG, Miller JJ. Eczematous Rashes. In: Lookingbill & Marks’ Principles of Dermatology. 4th ed. Elsevier Inc; 2006:105-108.
Wolff K, Johnson RA. Eczema and Dermatitis. In: Fitzpatrick’s Color Atlas & Synopsis of Clinical Dermatology, 6th ed. McGraw-Hill;2009:20-33.