Cold Sores

Unlike bacterial infections such as pink eye, you cannot get rid of cold sores with medication, since they are caused by the herpes simplex virus. Usually appearing as small, fluid-filled bumps on the skin near the mouth and lips, cold sores can appear up to 20 days after you are exposed to a person carrying the herpes simplex virus [source: Mayo Clinic].

Diseases Spread Through Makeup

Although a group makeover can seem like fun at the time, an outbreak of pink eye or another infection is not. Diseases aren't just spread through close friends; you can also pick them up if you use the tester products at the local beauty counter, or if you have a department store makeup consultant give you a makeover. In fact, one study found staph, strep and E. coli bacteria in department store makeup tester products [source: Wu]. Without safety precautions, a carefree makeover day can turn into a visit to the doctor.

One potential, and particularly pesky, result of sharing eye makeup is getting pink eye, also known as conjunctivitis. This infection of the lining of the eyelid results in red, itchy, watery eyes and can last for up to two weeks [source: Mayo Clinic]. Pink eye is very contagious, so it is easy to spread among people sharing the same makeup. If you come down with this disease, a doctor can prescribe medicated eye drops to clear it up within a few weeks, but you won't be able to wear eye makeup or contact lenses in the meantime.

Swapping lipstick with a friend who is infected with the herpes simplex virus, which causes cold sores, can pass the virus on to you. You can contract herpes even without visible cold sores present on the infected person -- and remember, there's no cure for the herpes viruses. Just one incidence of sharing your lipstick can lead to a lifetime of contending with the condition if you contract the virus.

In addition to keeping your cosmetics to yourself, ensuring that what you own is still in working order can also prevent disease. Keep reading to learn how to avoid makeup contamination.