The fountain of youth of the '90s may be as close as the nearest cosmetic counter -- in the form of new, acid-based skin-care treatments. These face-saving formulas first trickled onto the market three years ago. Today, they still pack a powerful punch as companies continue to debut more acid-laced compounds.

Dermatologists have prescribed alpha-hydroxy acids (AHA) and other acid ingredients to patients for years. Prescription-strength formulas get rid of scaliness, while acid concentrations of 30 to 70 percent perform deep skin peels that remove scars and wrinkles.

In the last two years, the beauty industry has begun touting its own nonprescription acid formulas. This trend has been a financial boost to the skin-care category.

"Alpha-hydroxy acids are natural substances that provide the anti-aging benefits and results of Retin-A without some of the possible, harsh side effects," says Ann Grazseth, merchandise manager of cosmetics for J. C. Penney Co. Inc. department stores.

Blame it on the baby boomers' search for eternal youth. The average age of users hovers at 35 years old, though most companies claim customers ranging from 16 to 70.

"These acid products are the single largest growth category in skin care today," says John Stabenau, divisional merchandise manager for cosmetics at Neiman Marcus. "This is not just a perceived miracle in a bottle -- you actually see results."

Alpha-hydroxy acids create a smoother skin texture through exfoliation. They penetrate the skin and weaken the bonds that hold dead cells together in the skin's outermost layer. When the older skin is sloughed away, younger, plumper, less wrinkled skin emerges.

"Up to this point, there hasn't been anything on the market like this," says Gary Jones, Product Marketing Manager for Dallas-based BeautiControl Cosmetics. "These products make claims they can keep, and it doesn't take long to see the results."

According to cosmetic companies, a woman will see a dramatic difference in her skin after using an acid product for four to six weeks. These formulas work to improve older skin's clarity while softening lines and wrinkles. They eliminate flakiness in dry skin while helping it retain moisture. By removing dead skin cells and pore-clogging debris, these acid products also help neutralize oily skin.

"We've had women tell us that our product has helped reduce pregnancy masks, fade age spots and lighten scars," says Mr. Jones.

For African-Americans, AHA products can help reduce ashiness, the white cast caused by dry skin cells. "Women of color have seen tremendous improvement with Fruition," says Peter Lichtenthal, executive director of treatment marketing for Estee Lauder. "We've seen over 80 percent reduction in ashiness."

Even men anxious to turn back the hands of time have discovered AHA products. To respond to this market, companies such as BeautiControl and Aramis have created male-friendly acid products. Others, such as Estee Lauder, advertise the same products to both sexes.

"Lift Off! was developed specifically for a man's skin, which is oilier and thicker than a woman's," says Amy Mayfield, publicist for New York-based Aramis. "It's a more concentrated formula that also has a moisturizer" and Sun Protection Factor 7.

For cosmetics companies, the promise of dramatic results translates to big bucks. "Fruit acids have impacted skin care like nothing else," says Mr. Lichtenthal. "Fruition has been the single most successful launch in our company's history."

Other companies boast similar success stories. Avon's Anew Perfecting Complex for Face racked up sales of $70 million worldwide the first year it was introduced. In the first four months of its launch, Mary Kay Cosmetics sold 35 million units of its Skin Revival System.

With so many companies dropping acid products into the market, it's easy for the consumer to get confused. There are serums, creams and lotions in single, double or triple-acid formulas. Labels read like chemistry projects. Acid percentages vary from two to 10 percent.

While there is currently no federal ruling on how much acid a cosmetic company can pack into a compound, most keep their concentrations at less than 12 percent. "At lower concentrations, these acids can be used at home safely and effectively for cosmetic use," says Myra O. Barker, chief scientific officer for Mary Kay Cosmetics. "We aren't trying to develop a peel here, we're creating micro exfoliators."

Acid choice also depends on where you plan to use it. "It's not just the percentage of acids that you have to look at, it's the pH level and the formulation," says Janice Teal, director of Avon skin-care laboratories. "Different parts of the body also respond differently to these acids." Skin with more sun photo-damage, she says, "may need an intensive-strength formula, while the more sensitive neck and chest needs a milder one."

Prices range from less than $10 to more than $100.

To reap the anti-aging advantages long-term, you must continue to use the product. "Your skin turns over every 28 days," says Dr. Teal. "After a month or two, your skin will lose the benefits of the acid products."

WHERE TREATMENTS COME FROM

You don't have to be a chemistry major to understand the basic ingredients in the latest skin treatments. These scientific substances actually boast more humble beginnings. Alpha-hydroxy acids are derived from natural substances such as fruit, milk and sugar cane.

Citric acid -- Derived from citrus fruits

Glycolic acid -- The smallest AHA; from sugar cane

Tartaric acid -- Produced from old wine

Malic acid -- Cultivated from apples

Lactic acid -- Developed from sour milk

Salicylic acid -- While not an alpha-hydroxy acid, salicylic acid is PTC an active ingredient in several skin treatments. This acid can be derived from the willow tree or manufactured synthetically.

DO'S AND DON'TS

Only buy an AHA product from a reputable company that can provide full information, has thoroughly tested its product and will stand behind its claims.

* Sample products to find the formula that works best for you. If you have very sensitive skin, minimal sun photo-damage or few fine lines, opt for a lower-percentage acid formula.

* If you have more wrinkles or thicker, more damaged skin, try an intensive product. If irritation occurs, shift to a formula with a lower acid concentration.

* Apply to clean, dry skin once or twice a day, depending on your individual skin condition. Everyone is different. Experiment to find what works best for you.

* Don't get these acid products into or on your eyes. While these cosmetic compounds won't blind you, they will cause your eyes to burn and sting.

* Don't slather on these products. Instead, follow the less-is-more philosophy to avoid irritation.

* Dry skin with fine cracks may experience some slight irritation at first. AHA products can cause a burning or tingling sensation as they slip through these cracks. After two weeks, as the skin becomes more pliant, these micro-fissures should heal and the irritation disappear. If irritation continues, consult the skin care representative from whom you bought the product.

* AHA products can be drying. Follow each application with a moisturizer designed for your skin condition.