I went to a new dermatologist the other day to check out a thing growing on my thigh. My totally non-medical husband had diagnosed it as just a blood blister, but I didn't want to take any chances. It was black and scary-looking, and I wanted to get it seen by a professional.

At least, I thought it would be seen by a professional, someone whose interest was more in the science than the art -- or the business -- of skin medicine. But apparently you can't take such a thing for granted anymore. These days, you may think you're in the middle of a medical encounter, getting medical advice from a physician, but suddenly what you're in the middle of is an infomercial, and your doctor is trying to sell you something expensive and entirely cosmetic. There were moments, during my session with the dermatologist, when I thought I had stepped out of a doctor's office and into an Elizabeth Arden day spa.

This sense of a shifting boundary between physician and beautician first hit me when the dermatologist walked into the examining room. With her white coat thrown over a chic pair of slacks, and her impractical pointy shoes, she wasn't even dressed like a real doctor; she could have been a cosmetician. And she was gorgeous. Her skin was what I noticed first: honey-colored and velvety, smooth as a china bowl, not a wrinkle or pore to be seen. I always look at skin when meeting a new dermatologist. Usually I find myself thinking, If he's so smart, how come he looks so bad? But with this doctor, what I basically thought was, Is she airbrushed? She had the kind of intimidating looks you expect to run into at, say, a hair salon on the Upper East Side.

Dr. Fashionista diagnosed the growth on my leg as a harmless blood blister as soon as she saw it. Still, she figured she should take a biopsy just to be safe. Two hundred bucks. Then she figured she should take a biopsy of something on my left shoulder that she didn't like the looks of, even though I told her the looks hadn't changed for more than a decade. Another 200 bucks.

Then she figured she should give me a full body check, since I'd never had one before. What a full body check amounts to (besides $275) is me with my clothes off and her examining various parts of me and calling out to her assistant, who writes it all down, "Face, light freckling; arms, heavy freckling; legs, spider veins." Hey, don't they teach these people some fancy word for spider veins that's a little less blunt? At least she was delicate enough to call my age spots "lentigo." Still, the full body check didn't do much to improve my feelings of overall appearance- angst.

I knew enough from my years of medical reporting to recognize that the flaws she was enumerating, all those freckles and lentigo, were signs of sun damage. So I was in perfect patsy position when she offered her next observation: "You have sun damage on your face." Well, of course I do. I'm 50 years old, and my face goes outdoors.

But I don't sunbathe, I wear sunscreen on my face even in winter, and for years I've used Retin-A, which supposedly reverses sun damage. I even wrote a book called "How a Woman Ages" that included exhortations to avoid the sun -- and, with rare exceptions, I've followed my own advice. In my more lucid moments, I know that whatever is going on with my face these days, in terms of crow's-feet and wrinkles and uneven skin tone, isn't only about the sun. But I didn't have my guard up sufficiently with this dermatologist. I was there because I thought I had melanoma, so when she started talking about sun damage, I paid attention.

And this doctor wanted to fix my sun damage. She said she could give me a chemical peel. "Isn't that a little extreme?" I asked, remembering the horror stories I'd encountered researching my book 20 years ago, chemical peels that were essentially acid burns that made the skin blister, crust and flake off. Sometimes it led to smoother skin, but other times it resulted in mottled, discolored faces.

"Not anymore," she said, ramping up the infomercial. She'd been rather laconic up to this point, but now the words came tumbling out. She told me about a product that causes a more controlled peel, mentioning the word "collagen," which is big in women's magazines these days. For good measure she also mentioned the word "cancer." This new peel, she said, gets rid of early skin changes, which might in turn become early lesions, which might in turn lead to skin cancer.

"So are you recommending this for medical reasons," I asked, "or cosmetic reasons?"

"Well," she said, "there's a very blurry line between the two."

No, there's not. My insurance company will pay for a medical procedure, but it won't pay for a beauty treatment. Preventing skin cancer is medical. Getting rid of fine lines and wrinkles -- and she actually called them "fine lines and wrinkles," just like the ads do -- is cosmetic.

Still, I asked: "How much?" It turned out to be $200 -- not bad, I guess, same as a biopsy. Ah, but that's just $200 each time. This doctor would like me to have a chemical peel every single month for at least six months, maybe more.

I should have seen this coming. Just last month I saw an optometrist because I lost a contact lens, and he wanted me to think about corrective surgery instead of contacts, even though it probably wouldn't work on eyes like mine -- my pupils are too big -- and he knows it. But surgery is no doubt a much bigger moneymaker for him than old-fashioned contact lenses are, so I guess he figured it was worth a pitch.

When did it happen that medical people started hawking beauty products? In a doctor's office, we're not steeled against the hard sell the way we are walking through the perfume department of Bloomingdale's. Even I, a skeptical medical reporter, managed to get taken, at least a little bit, by my gung-ho dermatologist. As a parting salvo, she switched channels on the infomercials and declared I'd been using the "wrong" sunscreen. Lucky for me, her office imports a far better sunscreen, otherwise available only in France.

I'm ashamed to say I bought it. I have no idea why. I guess the doctor had made me feel ugly and sun-damaged, and I thought this would be an easy way to fix me. And it would get me out of her office before I felt the need to sign up for a prescription moisturizer or, God help me, Botox.

But I won't say how much I paid for it. I won't even tell my husband, the guy who correctly diagnosed the blood blister that got me into this mess. And he, bless his heart, hasn't pressed me. I guess he knows a face-saving gesture when he sees one.

Author's e-mail:

henigoutlook@yahoo.com

Robin Henig, the author of "Pandora's Baby: How the First Test Tube Babies Sparked a Reproductive Revolution" (Houghton Mifflin), is a New York writer who bears a distressing resemblance to the "before" pictures in plastic surgery ads.