A woman in the US is suing a cosmetics store because she claims that she caught herpes from their lipstick tester. In case you’re wondering if this is even possible, as a microbiologist, I can tell you that it most certainly is. And it’s not just herpes that can lurk in makeup.

But let’s look at herpes first.

This very common virus is mainly spread by skin-to-skin contact, kissing and sex, but it can also be transmitted in droplets of spit left by an infected person on towels, cups, cutlery and, yes, lipstick. Globally, it’s estimated that 67% of people are infected with the Herpes simplex virus (HSV-1). But it’s a hidden enemy – a person doesn’t need to have visible signs of the virus to spread the infection. The virus lives in facial tissues where it can shed and spread.

It doesn’t always show up on the skin as a blister immediately after it has infected a person, instead it can stay hidden and appear after a few months. Because of this, it’s impossible to say with certainty if the American woman caught herpes from this particular store tester, or elsewhere.

Herpes causes blisters on the lips and around the mouth that can last up to ten days. Lipsticks and makeup brushes that touch these parts of the face can then spread the infection to other people.

Fortunately, herpes is a fragile virus and typically only survives outside the body for ten seconds. But it can survive longer in warm and moist environments, such as in sweat. It can also survive between two to four hours on plastic, chrome and water, so there are lots of ways the virus can spread.

There is no cure for a herpes infection, although treatments are available that will reduce the length of infection.