Heat As a Cause?

Hard to tell what organism are responsible for S.D. in your case, however, sun exposure and moisture are two common factor.

For sun exposure I would try applying an antifungal remedy such as lavender oil mixed with a sun screen solution. The lavender oil is both antifungal and anti inflammatory.

If the reason is due to moisture and humidity, however, most of India, the weather is dry, but there might be some exceptions, then a 1% H2O2 solution applied to the area several times a day would kill the fungus and dry the skin.

If sun is a factor, which a more likely case, I would use sun umbrellas or a cap to prevent the sun from reaching the face. I have seen cases of S.D. where sun exposure is the cause since it only occurs in areas or parts of the body that is exposed to the most sun, that area usually is the face. Sun screening therefore, in practice will help, there are many products so I suggest trial and error and look over a couple of brands, since they don't work the same way due to differences in ingredients. If I am short on cash I make my own, such as a solution (in water) of zinc oxide (or titanium dioxide), or sometimes vitamin E (only the kinds they used where you take it internally) and applied to the face. However, if sunburns is partly responsible, aloe vera oil or lotion may work, but those are applied after sun exposure while sunscreen lotion are applied during the day. It takes a week to notice no increase in S.D. and a slowly decrease in such conditions.

Whichever the cause, I would also check for urinary sugar and urinary pH, sometimes excess sugar (they happened a lot in hot climate) as a result of dehydration may cause the body's immune system to be lowered, in which case a simple water with a small amount of sea salt would help. In this case one liter of water mixed with 1/4 teaspoon of sea salt will correct the electrolytes, pH somewhat, and diluting the sugars. Usually the normal urinary sugar is about 2% and should never exceed 5% in hot weather, if they do a skin problem, tends to occur whenever urinary sugar exceeds 5% or more. I tend to rely on maximum urinary sugar to gauge my health, rather than minimum blood sugar (fasting) as the former detects early warning rather than late warnings as used in blood sugar. Of course that's my opinion, which seems to work and a simple remedy if sugar is the cause is drinking more water whenever exposed to the sun.

Finally certain vitamins are essential, especially antioxidants so the skin can withstand the free radical effects of the sun, such as vitamin A, vitamin E, and vitamin C, and sometimes B complex.