Silicone caulk is your first line of defense, but that should be considered a stopgap fix only. Leaking shower walls implies a bigger problem - it should probably be checked out by a plumber. Letting it go could result in structural damage to your house.
What is wrong with the shower handle? Loose? Too tight? Leaking? Not working?
Remove and replace.
get a plumber :L
If it is leaking from the control, you should be able to access that from the front. If it is the supply lines or the pipe to the shower head, there may be access behind it in a closet. If not, you just have to cut a hole to get to it.
If it is leaking when you use the shower, not shutting off completely, it will need to be replaced. If it is leaking at the wall, take it off and reseal the thread on the pipe with either pipe dope or Teflon tape and reinstall.
If it is indoors and not a recessed shower, you may have a leaking shower pan.
A leaking shower valve by installing a new cartridge.
Usually this is just a matter of changing the rubber washer. This joint should only require hand tightening.
If it is galv. pipe there could be a small hole on threads. You would have to replace pipe.
The most common material used on shower walls is Fiber glass. Fiber glass is the most common material used on shower walls because of it's durability.
Steam from your shower can indeed effect the bathroom walls. You should wash your bathroom walls on a regular basis. Mold can grow from excess water or even the steam from your shower.
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