They usually begin as flat, but parts may raise above the skin surface.
As cells move toward the skin surface, they start dying.
Any part of the skin surface can be involved.
They do this to ensure the least amount of damage possible to the skin surface.
As a result there is very little visible at the skin surface.
Light pressure is needed to feel the tissue close to the skin surface.
These cells form the hair in the root and then grow through the skin surface taking any substances with them.
As such, anything that keeps the skin surfaces dry will end the problem.
Actually, it is not the sweat, but the evaporation from the skin surface.
"What about markings on the skin surface near the heart?"