We've all had our moments with mysterious skin ailments. But distinguishing true contact dermatitis from other skin ailments takes some detective work.

Contact dermatitis is associated with blisters, redness, and itching -- but only at the site of exposure to a toxin or allergen. Common culprits include a recent change in body soap or laundry detergent, as well as new jewelry (especially if there's nickel in it) or a new perfume. If removing the potential trigger removes the symptoms, bingo! Mystery solved. Still itchy and red? Take this symptom checker for psoriasis.

Contact dermatitis has several other names, including allergic dermatitis and just plain old dermatitis. The classic example of contact dermatitis is the reaction most people have to poison ivy, poison oak, or poison sumac. Simply stated, contact dermatitis is skin inflammation due to exposure to an irritant or allergen -- be it the oils from a poisonous plant, the metals in a cheap piece of jewelry, or the constant noogies from an obnoxious older brother.

It will often clear up on its own when the irritant is removed. But you can ask your doctor or pharmacist to set you up with a topical itch cream to make life tolerable while you wait for that to happen.

Now, a cream for an annoying older brother? That's another story.

YOU: The Owner's Manual. Roizen, M. F., Oz, M. C., New York: HarperCollins, 2005.