What Causes The Mustache To Become White Pasty Hair?

Hello Doctor,
I have the problem in mustache (becomes white pasty hair and once wipes there will be patches) small patches which seems smooth but I am not really feeling my mustache falls, but after some time it looks normal and again it repeats.

I feel after some time my mustache will be having more gaps with smooth effect.
what is the root cause for this and is there any