It has long been noticed that one side effect of the glaucoma drug Lumigan (bimatoprost ophthalmic solution; Allergan) is increased eyelash growth, however, nobody could have predicted that cosmetic companies would start using small quantities of prostaglandins in products specifically designed for the "beauty" market.

Allergan itself is believed to be testing the drug for lash enhancement but other, enterprising cosmetic companies have beaten them to it. Two examples of such products, "Age Intervention Eyelash Conditioner" manufactured by Jan Marini Skin Research and "RevitaLash" made by Athena Cosmetics Corporation, are already on the market.

In response, Allergan has filed a patent-infringement suit against several beauty companies, including the two mentioned previously, that it says use a prostaglandin in their products. Although it declined to discuss its own drug development plans in this area, Caroline Van Hove, an Allergan spokesperson, commented "We've got intellectual property in this particular area."

These disputes demonstrate how unclear the line between cosmetics and drugs can be since cosmetic products can use ingredients that are also used in prescription medications. However, FDA regulations state that, if a company promotes its product to change the structure or function of the body, rather than just its appearance, then it is classified as a drug and must prove its safety and efficacy in human tests.

The FDA has so far declined to comment on how its rules apply to cosmetic eyelash products.