Teaching was enough to make Victoria Knight-McDowell sick. "Just as I would get over one cold, I'd catch another," she says of her sneezy, wheezy winter as a student teacher in 1995. "Every time I would see a child with sniffles, I wanted to back away. But you can't do that."

Instead of giving kids the cold shoulder, Knight-McDowell—who grew up being dosed with herbal remedies brewed by her mother—decided to wage her own version of germ warfare. With encouragement from husband Rider, a freelance writer, and Internet research on Chinese medicine, she began blending mixtures of herbs and vitamins in the kitchen of their Carmel, Calif., home. Using family and friends as guinea pigs, Knight-McDowell, 44, eventually devised the potion—including zinc, forsythia, echinacea and vitamins C, E and A—which she and Rider, 43, started to market as Airborne in 1997.

Although it's carried by big drugstore chains like CVS and Rite Aid and ranks as the top-selling herbal cold remedy on drugstore.com, whether Airborne actually does prevent colds remains an open question. Those who swear by it include actor Kevin Costner ("I believe Airborne works; I have it on my private plane "). Physicians such as Dr. Peter Katona, a specialist in infectious diseases at the UCLA School of Medicine, sniff at such claims. "People are wasting a lot of money," he says of the tablets, which cost $7.95 for a 10-pack, "on something that's completely unproven."

Even if she hasn't come up with a pharmaceutical magic bullet, Knight-McDowell—who juggles running her company and working as an occasional substitute teacher with raising son Errol, 4—does seem to have found the formula for success. Though you wouldn't know it from the family's still-modest lifestyle—including a 1992 Volvo wagon—Airborne, buttressed by a campy ad campaign featuring throwback TV personalities like Barry Williams (The Brady Bunch), posted gross sales of $10 million last year. Cold comfort indeed.