The top three skin conditions are surface bacterial infections of the skin, mange (scabies) and fungal infections of the skin. Those are roughly in order of frequency but there is much noise based on local conditions.
Mange is very itchy. What starts as mange often ends up with a bacterial infection.
Bacterial skin infections sometimes infect deeper tissue and become life threatening.
|Their terminology is different than mine. Pyodermia is the bacterial infection, Scabies is mange and tinea is fungal.
Studies yield conflicting information about sanitation: Is soap important, is the amount of water used a critical variable, is the quality of the water a variable, is it important to have disinfectant in the soap or water, frequency of bathing, time of washing? None of the studies investigated frequency of laundering.
Skin conditions vary by season. Heat and humidity are not your friend.
***Edited to add, mange is caused by tiny mites that burrow into the skin and are spread by touch. COLD weather can increase mange if multiple people sleep together for warmth, but not always with the same people each night.
Near the end of the report a list of "critical drugs" is given. I was surprised to not see lime-sulfur preparations for mange. It must not be profitable enough.
"Not scratching" and clean hands and fingernails will be marks of refinement and indicators of high life expectancy.
As always, prevention is your best bet.