Flat warts can spread across your body. One of the ways they do so is when you shave over an infected area and then nick an uninfected area with the razor. If you have a growth of flat warts in an area where you can tolerate hair growth for a while, you might want to avoid shaving until the outbreak is taken care of. If abstaining from shaving is not an option, try to use new, good-quality razors to minimize nicks.
Another way you can prevent new growths of flat warts is to build up your immune system. Because the warts are caused by the HPV virus, they will stick around until the infection is conquered.
The next treatment method is harder than it sounds.