Many head lesions are caused by fungus.

Using Nizoral shampoo may help this. Also washing hair less frequently may work as fungus loves moisture.

People who sweat heavily, or wear caps alot, are more prone.
Once the fungus gets going it can be very resistant to cure, because it lives in the deeper areas of the skin.
This is similar to tinea versicolor on the skin, which is very hard to get rid of as well.

Diabetics and people with reduced immune functions often get skin fungal infections commonly.

My son found T-gel very effective...but I worry because coal tar products have been found to cause skin cancer. For this reason coal tar products are so not commonly prescribed by dermatologists as in the past.

Also being low in zinc in the diet negatively affects the skin and hair.
Many dandruff shampoos have zinc in them for this reason.
Some drugs will deplete zinc heavily, so taking zinc supplements for those people is very helpful.