Q. While riding to work on Metro, I've frequently noticed people listening to radios with headphones. Often, the sets are turned up so high that even though I am sitting some distance from the individual wearing one, I can clearly hear the sound. Does playing loud music through headphones like this cause any appreciable hearing damage?

A. The answer to your question is a loud, "Yes!"

Noise can damage your hearing either temporarily or permanently. The amount of damage depends on how loud the noise is and how long you're exposed to it.

Noise is measured in units of decibels. Each 10-decibel increase reflects 10 times the intensity of sound. Continuous exposure to noise above 85 decibels can be hazardous. Examples of 90 decibel noises are power tools, lawn mowers and stereo headphones at moderate volume. Noises at 100 decibels -- 10 times louder than 90 decibels -- include chain saws, jack hammers and loud stereo headphones.

Noise is loud enough to damage your hearing if:

You have to shout over background noise to make yourself heard.

The noise hurts your ears.

The noise makes your ears ring.

You are slightly deaf for several hours after exposure to the noise.

Listening to headphones at 90 decibels for more than an hour or two can lead to temporary hearing impairment; longer durations can cause permanent hearing loss. Levels as high as 120 decibels -- measured at rock concerts in front of the speakers -- represent an immediate threat to your hearing.

A common misconception is that you can adapt and "get used to" loud noise. However, what appears to be a lessening of noise over time is actually a sign of hearing loss. Loud noises don't sound as loud anymore, not because you've "adjusted" to them but because your hearing has been damaged.

Parents seem to have particular trouble getting their teenagers to turn down loud rock music. Even without headphones, playing music very loudly in a room can harm their hearing. You can try telling them that loud music is bad for their hearing, but don't be surprised if your pleas fall on deaf ears.

For a free booklet on "Noise, Ears and Hearing Protection," send a self-addressed business envelope to the American Academy of Otolaryngology -- Head and Neck Surgery, 1101 Vermont Ave. NW, Suite 302, Washington, D.C. 20005.

Q. I'm a 38-year-old woman and have been on high blood pressure medication for about four years. Several months ago I began noticing a darkened line around my neck. Lately, this area has begun itching, along with a newly formed dark, itchy area around my wrist where my watch is.

Do you have any suggestions for getting rid of these unsightly skin conditions? I think I must be reacting to my blood pressure medicine, but am afraid to stop taking it.

A. I'm not sure you need to stop taking your blood pressure medicine to clear up your skin condition. Besides being allergic to your medicine, there are several other skin disorders that could be causing the rashes you've described. The most likely is some form of contact dermatitis, a reaction to something on your skin. The clue to this type of reaction is its characteristic location or shape.

There are three types of contact dermatitis: 1) irritation, 2) sensitization, and 3) photo-sensitization. Irritation reactions make your skin itchy and red within minutes to hours after coming into contact with an irritating substance. An example is propylene glycol, a solvent used in cosmetics to make them feel smoother.

Sensitization reactions are responses to something you're allergic to. Poison ivy -- a substance most people are allergic to -- is a familiar example. After repeated contact with an allergic substance, your body becomes "sensitized" to it and reacts against it. Many people are allergic to nickel, and if this metal is in your necklace or wristwatch, it could cause the kind of skin reaction you describe.

Photo-sensitization reactions are an unusual form of allergy. Instead of your skin reacting directly to the provoking substance, it takes the ultraviolet rays of the sun to trigger this reaction. Some ingredients in perfumes and cosmetics fall into this category. You can put on the perfume without any problem, but any area of your skin also exposed to sunlight may react by becoming red, later turning dark.

Your neck rash could be a photo-sensitive reaction to perfume or other cosmetic. It's also possible that your blood pressure medicine is causing this type of reaction. If so, only the parts of your body regularly exposed to sunlight, typically the neck and forearms, will break out.

Other common substances that frequently cause contact dermatitis include rubber and elasticized garments, hair and fur dyes, nail polish, leather, ethylenediamine (a preservative in creams and eye drops) and dichromates (used in textile ink, paints and leather processing).

You have to play detective sometimes to figure out what your skin is reacting to. For example, if you notice a band-like skin rash under the strap of your leather sandals, it's a good bet that your sensitive to something in the leather. With contact dermatitis, it may take some trial and error testing to pinpoint the offending agent, but if you can find it, you've solved your problem and avoided others in the future.

Jay Siwek, a family physician from Georgetown University, practices at the Fort Lincoln Family Medicine Center and Providence Hospital in Northeast Washington.

Send questions to Consultation, Health Section, The Washington Post, 1150 15th St. NW, Washington, D.C. 20071. Questions cannot be answered individually.