its from living in a humid enviroment,eating too many fermented products,sugar,wheat,starches and not enough veggies to push out the crap.
try neem soap and shampoo on him. it really helped.
also saylic acid (clean and clear face cleanser has it )helps kill it topically.
have him use a scrubby brush on his skin.
and clean up his diet of all the yeast causing foods. if that doesnt work perhaps a Bowel Cleanse will be in order.
i also did a herbal parasite cleanse.
i did all this and it cleared up my condition that i was fighting for 5 years. even scrips did nothing because it came back until i took the preventative measures of addressing my crappy diet and dirty intestines.