The actress Barbara Hershey did it. So did a 48-year-old office manager in Manhattan as well as dozens of celebrities who won't admit to it: television anchors, Broadway performers and film stars who arrange after-hours doctors' appointments so they won't be recognized in the waiting room.

What they're all doing is having their faces injected with collagen, a smooth white lotion that looks like hand cream and can be shot through a slim needle placed just beneath facial skin to "plump up" the lines and furrows that come with age. It can also make lips fuller and smooth out surgical and acne scars.

Collagen made Barbara Hershey look like she'd been kissed by a bee in the 1989 movie "Beaches." And it made the Manhattan office manager look so much younger after her first two treatments in 1988 -- she has had three subsequent touch-ups -- that, she says with a laugh, "I finally had the guts to throw my husband out."

But despite its beauty-enhancing qualities, collagen makes some federal health officials nervous.

Nervous, too, are a few influential members of Congress, who began investigations into the collagen boom earlier this year. The results of those efforts raise questions about the anti-wrinkle shots.

As Rep. John Dingell (D-Mich.) wrote in a recent report by his subcommittee on oversight and investigations of the House Energy and Commerce Committee, leave 2 lines open for quote tk

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"I am tired all the time, I have scars on my face . . . severe muscle and joint pain, recurring rashes on my eyes, neck and face," Wanda Stone Mayberry of Nashville told Dingell's committee in a recent letter. Mayberry, tk, said her problems stem from the collagen injections she had been receiving on a regular basis for tk years.

Not every collagen patient feels the way Mayberry does. Many are enthusiastic, like the Manhattan office manager who asked that her name be omitted because she has not told friends about her treatment. Her dermatologist, Nelson Lee Novick, is equally pleased. "I've been using collagen for the past nine years, and the vast majority of my patients are satisfied," said Novick, chief of the dermatology clinic at New York's Mt. Sinai Medical Center. "It's the only procedure that gets rid of wrinkles and scars, especially in the middle of the face, that even a face-lift can't smooth out."

Physicians also wrote to Dingell, extolling the virtues of collagen and re-affirming their confidence in its safety. Wrinkle removal is not collagen's only virtue, they contend. Terry W. Marsh, a dermatologist in Muncie, Ind., described one young patient whose face was so pitted friends called her 'Scarface.' "As you can imagine, these taunts have been psychologically devastating," Marsh wrote to Dingell's committee. After successful treatment with collagen, her self-esteem improved markedly. "I realize that injectable collagen is not 'lifesaving' or 'life-prolonging.' However," he wrote, "collagen treatments can most definitely be 'life-enhancing.' "

And that is why more than 500,000 people have received collagen injections since 1981, when the cosmetic therapy was approved by the Food and Drug Administration.

Protein Power. A protein found in the skin of all mammals, collagen provides a structural framework for skin, bones, ligaments and cartilage. Collagen makes up about one third of the protein in the human body.

Because it is so essential to the elasticity and shape of the skin -- and because it declines with age -- collagen was promoted for years as an important ingredient in certain moisturizers and wrinkle creams. But it is a large molecule, and when mixed into an ordinary lotion, collagen cannot penetrate beneath the skin's top layer of dead cells. That blocks its effectiveness as an anti-wrinkle agent.

Injectable collagen is different. Like spackle applied to a chipped wall, it can be delivered to the inside of a wrinkle or scar and will fill in the depression until it meets the contour of the surrounding skin.

Zyderm, which is derived from the collagen of cowhide, was the first form of injectable collagen to receive FDA approval. It has roughly the consistency of body lotion. A related substance, Zyplast -- which is noticeably thicker, more like a heavy-duty night cream -- was approved for cosmetic use in 1985. Both are manufactured by The Collagen Corp. of Palo Alto, Calif.

Among the areas most often treated with Zyderm and Zyplast are the nasolabial folds -- the lines running from the sides of the nose to the corners of the mouth -- and "smoker's lines" -- the tiny vertical wrinkles above the upper lip.

A handful of patients have recently been receiving collagen injections to make their lips look fuller and poutier. This is considered "augmentation" -- and exceeds FDA approval, which is limited to the correction of "contour deformities" such as wrinkles and scars.

Like most cosmetic procedures, collagen shots have side effects. They can cause local inflammation, including red welts, infection, allergic reactions and irritation that persists for six months or more.

In addition, doctors know that the body gradually metabolizes the animal-derived protein so that the cosmetic effect eventually wears off. As a result, injections must be repeated every few months for the benefits to last.

Patients are advised that these additional injections are necessary to keep the skin smooth. In the early '80s, The Collagen Corp. said that "touch-ups" were needed about once a year. By 1989, officials advised two such treatments annually; currently, product promoters say they are required about three or four times per year. The company says that collagen shots are a lot like hair color or leg waxing -- "maintenance" beauty routines that women should plan to undergo every few months.

Collagen "touch-ups" can be expensive. The first series of injections can cost from $200 to more than $1,000, depending on the area treated, and each follow-up treatment can cost nearly as much.

Health Effects. The Collagen Corp. requires that prospective users receive a trial dose under the skin of the forearm to test for allergies. Those allergic to lidocaine, the local anesthetic in the collagen preparation, are automatically excluded. If no local reaction is detected within four weeks, a physician can assume it is safe to inject collagen into the face.

But according to several dermatologists and plastic surgeons who have communicated with Dingell's subcommittee, continued re-exposure to collagen might sensitize the individual in ways that did not result from the initial skin test. What most concerns these doctors is the possibility that repeated exposure to an animal protein might stimulate a reaction that eventually causes a patient to mount an immune response against the body's naturally produced collagen.

This can happen, they say, even in those who passed the sensitivity test and had one or two Zyderm treatments with no ill effect.

A few small studies have linked injected collagen to several autoimmune diseases, including scleroderma, lupus and a rare disorder called polymyositis/dermatomyositis (PM/DM). A direct cause-and-effect link has not been proved, but officials are cautious about possible long-term consequences in view of the increased use of collagen injections and the seriousness of potential immunological problems.

PM/DM is a progressive weakening of the muscles that eventually can progress to "difficulty raising the arms above the shoulders, climbing steps or arising from a sitting position," according to the Merck Manual, a standard diagnostic reference for doctors. Patients may eventually be bedridden or confined to wheelchairs. Because of muscle weakness in the throat and larynx, they may also experience difficulty speaking, swallowing or keeping food down.

"{My wife suffers from} swollen, inflamed joints; debilitating pain in her knuckles, hips and feet and an overpowering fatigue that requires her to sleep eight to nine hours a day just to function properly," said William A. Harrison of Houston in a letter to Dingell's committee. Harrison said his wife had needed only 5 1/2 hours of sleep a night before she started receiving collagen injections to remove her wrinkles.

Harrison's wife, name tk, was diagnosed with polymyositis, which affects not only the skin but also the nerves and muscles. Neither dermatomyositis nor polymyositis is curable, although the symptoms sometimes can be eased with steroids and other drugs.

Based on a smattering of reports of cases like Harrison's, the Texas State Health Department began an epidemiological review last year to see whether PM/DM could be linked directly to collagen injections. The results, however, are still considered equivocal.

"It doesn't seem like a raging problem out there," said Dick Chiacchierini, an FDA statistician, who conducted a review of 414,000 patients who received collagen injections. The FDA, he said, was able to clearly document only nine cases of PM/DM among collagen patients, who are predominantely white and female, the number CDC said would be expected, even if they were totally unrelated to collagen. In order for the PM/DM cases to be considered statistically significant, Chiacchierini said, at least 15 cases would be required.

Adding to the confusion is the difficulty of diagnosing PM/DM. According to Jeffrey P. Koplan, an epidemiologist with the federal Centers for Disease Control in Atlanta and director of the CDC's Center for Chronic Disease Prevention and Health Promotion, the nine cases documented so far could signify underreporting. "Dermatologists might not be notified of PM/DM by their {collagen} patients," Koplan said in a recent letter to the FDA, "and rheumatologists diagnosing PM/DM would have no reason to link this rare disease to previous use" of injectable collagen.

The government remains concerned about the theoretical connection between Zyderm and autoimmune disease. "The investigation has gone as far as it can, given the data currently available," Koplan wrote, but "we continue to be concerned that this may be a real risk associated with these injections."

The Collagen Corp. advises people with pre-existing autoimmune disease not to use collagen. "If you have a personal history of autoimmune diseases, you cannot receive injectable collagen," the company's patient information booklet says. "These would include {but are not limited to} rheumatoid arthritis, psoriatic arthritis, scleroderma (including CREST syndrome), systemic or discoid lupus erythematosus or polymyositis."

But the company denies that collagen injections cause any autoimmune disease. Of the two lawsuits brought by dissatisfied patients against the Collagen Corp., according to Dingell's subcommittee investigators, both were resolved in the company's favor.

Regulating Cosmetics. Injectable collagen is classified as a medical device, not as a drug. There is some debate that because collagen is absorbed by the body, it should be re-classified as a drug and undergo further tests for safety and effectiveness. The product may well fall into a regulatory never-never land -- not quite a device like a pacemaker, not quite a drug like an oral medication.

Other treatments, such as silicone breast implants, also fall into this same gray area. Both collagen shots and silicone breast implants are largely used for cosmetic purposes. Both are inserted into the body and metabolized slowly over time. And both raise concern that a patient's immunological status may be affected several years later, though the risk has not been proved for either collagen or silicone.

Another concern about collagen involves the physicians who typically inject it. Most are dermatologists or plastic surgeons. But because anyone with an M.D. degree can legally perform any procedure on any patient, and because Zyderm is relatively easy to use -- it even comes in its own syringe -- collagen injections may be especially attractive to those who want to expand their medical practices.

"Clearly, Zyderm is an easy answer for the practitioner interested in financial gain, but without surgical qualifications," wrote a group of plastic surgeons from the Medical College of Virginia in the journal Plastic and Reconstructive Surgery. "We believe that the manufacturer has created a lucrative marketplace at the expense of the consumer for an agent the FDA should never have allowed on the market for uncontrolled use," they wrote. "We have grave doubts as to the long-term efficacy of this foreign protein in humans."

Everyone knows that beauty is not painless. But at what point is the pain excessive? When the goal is not medical but cosmetic, health officials are much more cautious about the potential for long-term health problems than if the products were being used to treat disease.

"In my opinion, it is not medically sound to be treating a cosmetic deformity with something with the theoretical possibility of altering something as deadly important as the immune system," said Erle E. Peacock Jr., one of the plastic surgeons who wrote the journal letter. "Especially when you don't get but a few months' improvement from it. I think it's a bad trade-off."

A satisfied user is likely to make a different assessment. "Now that I'm back out in the business world, I'm a lot more conscious of the way I look," said the Manhattan office manager. "And as long as they keep making collagen, I plan to keep using it."

Robin Marantz Henig is a Washington writer.