Watch out Bare Escentuals (NASDAQ:BARE) and Estee Lauder (NYSE:EL), there's a new kid on the market trying to smear your mascara.

On Friday, the Food and Drug Administration approved Allergan's (NYSE:AGN) Latisse, a treatment for hypotrichosis of eyelashes -- that means sparse eyelashes, for those not vain enough to know.

Small eyelashes are far from a small market -- the global market is around $3.7 billion. But Allergan is going to have a hard time capturing much of that market in this economy, considering the drug will run $120 a month. You have to look no further than how poorly cosmetic-laser makers like Syneron Medical (NASDAQ:ELOS) and Palomar Medical (NASDAQ:PMTI) have been doing over the last couple of years to see that beauty treatments are among the first things to be cut when the paycheck is in jeopardy.

But this economy will eventually rebound and Allergan could ultimately hit its target of $500 million per year in sales once the vainness returns. By comparison, Allergan is expecting nearly $1.3 billion in sales from Botox this year.

Ironically, Latisse was originally designed to treat glaucoma and is sold under the brand name Lumigan, but the longer eyelashes were discovered as a side effect. It's not all that weird to have the same active ingredient sold under two brand names. For instance Pfizer's (NYSE:PFE) Viagra is also sold as Revatio, a treatment for pulmonary arterial hypertension (PAH). The different packaging probably costs the companies a little money, but it avoids sending doctors a mixed message from their sales reps about drugs doing four different things like Eli Lilly's (NYSE:LLY) antidepressant-turned-fibromyalgia-treatment Cymbalta.

Being dependent on discretionary spending, Allergan is likely to continue to tread water until the economy improves, but investors thinking about the long term don't really need to worry about their mascara running; they can ride the waves without crying.

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