A New York City woman is suing MAC cosmetics claiming that she got herpes from the Rihanna-branded RiRi Woo lipstick, which she sampled at the singer’s May 7 show in Brooklyn.

The bright-red lipstick is the first in the RiRi Hearts line of cosmetics, which will also feature eye shadow palettes, brushes, and false eyelashes. On May 2, Rhianna tweeted that the lipstick was available for sale, and just three hours later it was sold out. That didn’t stop a pop-up shop at the Barclay’s Center from letting consumers sample the new color. That’s where 28-year-old Starkeema Greenidge says she contracted herpes.

In the lawsuit, Greenidge says that an employee at the store applied the lipstick directly to her lips after it had been used by another customer and the told her to “press her lips together and spread the lipstick around.” Two days later, her lips began to swell, she developed a cold sore, and was then diagnosed with oral herpes. Greendige is suing MAC for emotional distress and lost wages from the two weeks she was unable to work.

Two strains of the herpes simplex virus, HSV-1 and HSV-2, are responsible for oral and genital herpes infections.  Most often, HSV-1 causes oral infections and HSV-2 causes genital infections, though it is possible for HSV-1 to infect the genitals or HSV-2 to infect the mouth. Oral infection, which leads to sores on the lip that we tend to call cold sores, can be transmitted through kissing or oral-genital contact. The virus is most contagious when actual sores are present but can be spread in the few days before a sore appears when the virus is “shedding.” Though shared lipstick is probably not the usual method of transmission, herpes can be spread through objects that an infected person has used, such as infected razors or towels.

It remains unclear whether Greenidge really contracted herpes from the lipstick or if there is another source of her infection, but her case offers a reminder about some basic hygiene lessons for people trying on lipstick in a store: Experts suggest that before using a tester lipstick, you should wipe it down with a tissue or, even better, a tissue dipped in alcohol, and once it’s clean, use a cotton swab or other disposable applicator to put the lipstick on your lips. This advice applies to other make-up products as well. (Though herpes only infects the lips, mascara, eyeliners, and eyeshadows can spread pink eye.) One study found staph, strep, and even E. coli bacteria on tester makeup. So don’t apply anything directly from the package onto your face, and don’t use a store’s brushes, as animal hair can trap bacteria.