Pimples come and go, but warts—the small, rough growths that often sprout on hands and feet—are a more stubborn form of skin scourge. And you won't catch them from touching a toad: As SciShow host Michael Aranda explains in the video below, the bumps are caused by the human papillomavirus, the same kind of virus that can cause cervical cancer and other health problems, depending on the strain and the area of infection.

When you sprout a wart, it’s because the HPV virus penetrated your epidermis, or the top layer of your skin, through a tiny opening like a scratch. The virus causes epidermal cells to multiply, resulting in a coarse lump. (Those little black specks you notice on top of the wart are actually blood vessels, which provide the wart with food and oxygen.)

While you won’t contract warts simply by virtue of being a witch or stroking your little brother’s pet amphibian, you can catch them from skin-to-skin contact with someone who's afflicted, or by touching something a wart has also touched, like a towel or nail file. (This is why you should always wear flip-flops in a gym shower.) And once you have the HPV virus, it can also spread to other parts of your body, resulting in even more warts. That said, some people are more susceptible to warts than others. We don’t understand exactly why, but kids may be especially wart-prone because their immune systems are still developing.

For more information—including how to treat warts—watch the video below.