Very small risk in re-using the Latisse applicator
The Allergan company wants to MAXIMIZE sales of the product and minimize all lawsuits.
By law, they have to advise you on every thing that could go wrong (Have you checked the side of a ladder at Home Depot or Lowe's recently?), but in effect people can cut corners. Doing so takes away your cherished right to sue them.
Latisse is SUPPOSED to be applied at night AFTER you took off your makeup and washed your face. The likelihood of infection from using the same applicator on both eyes is...