Good morning Jack
To me it looks like a dry patch. Do you use any kind of lube when you masturbate. If not you may want to try some. Or it could be a rash type of thing. Have you changed any type of soap or something like that.
When you wash you just warm water. If it does not get better you may have to go to a doctor to have it check. It is better to be safe they sorry.
Take care Ken
the skin does look very irritated. do what ken below has suggested. and if you do use lube already maybe change it to a more sensitive one? allergic reaction maybe? if no improvement see the doctor.