1) I often have a bad taste in my mouth, and bad breath as well, I assume. This doesn't stem from poor hygiene: I brush my teeth at least three times a day, and usually more. I'm wondering if there is anything I can do about this. Could this be a symptom of some sort of nutritional deficiency? I think my diet is pretty bad, although I'm working pretty hard on getting more protein and eating less fat. I've also been nauseous a lot lately, and vomiting some. Could that be related?

2) Like many people, I often have an embarrassing bad breath. Listerine and other mouthwashes won't be of any help for this chronic problem. There are lots of products available to get rid of "volatile sulfur compounds (VSC)" - that supposedly cause this — and I just don't know which one I should try. Also, what's your opinion on tongue-brushing?

1) Which is better for you, tap or bottled water?

2) How bad is the water here in New York City? Do you recommend drinking filtered water, or does it really make a difference?

I've been swimming a lot this summer and I have noticed a green tint to my blond hair. Is this caused by previous dyeing? Is it possible to remove the green tint? Thanks for your time.

I have dandruff that responds well to over-the-counter shampoo. Ergo, I have been using the stuff almost exclusively for ten years. No brand in particular, sometimes zinc pyrithione (the blue stuff!), sometimes coal tar (the smelly brown stuff!). Anytime I switch to non-dandruff shampoo for like three to four days straight, I get my dandruff back. I worry that I might be addicted to dandruff shampoo. Should I worry?

Ever since high school, I've had very oily hair and skin, but it became worse in college. Now I'm in my mid-twenties and have to shampoo my hair about 10 times each day to get it clean. Then by evening it's already oily again. This isn't my scalp trying to moisturize itself after being over cleaned, because I've tried not washing it completely and it's even oilier the next day.

Are there any special shampoos or medications that help reduce oily skin? I've tried some facial products from my dermatologist, but they haven't reduced the oil production. This is an embarrassing problem and limits the overnight activities I can do, like camping or staying with friends.

What is the significant difference between a product that is antiseptic and one that is antibacterial? All of the antiseptic mouthwashes I find have a great amount of alcohol in them. This can be very irritating to the mouth. I have found one that is alcohol free, but it says it is antibacterial.

Thanks for your help.

I was wondering what causes fingernails to turn yellow if you leave nail polish on for a long time. Is it bad? And what can you do about it?

So far I have been extremely impressed by your service. I trust you with a question which I know many people share: Are whitening toothpastes detrimental to the longevity of one's teeth?