If your underarms are getting darker then you need to take some precautions for its treatment.

Avoid the usage of razor for removing hair and opt for the waxing method. Do not even use creams available for removal of hair.

Apply coconut oil on the underarms. Oil rich in Vitamin E would also be beneficial. You can also use baking soda after giving a wash to them.

Do not apply deodorant directly in the skin. It contains alcohol. You can use an alum powder as a replacement.

Application of lemon and baking powder on the underarms is another good treatment.

You can create a herbal supplement on your own for treating the problem of dark underarms. Make a paste using turmeric and cucumber. Add lemon to it and mix it properly. Then apply it for sometime on the underarms and wash it off after sometime.

Mix sandalwood with turmeric and gram flour to create a paste. Then add milk and lemon juice to it and apply. Keep it for 20 minutes and then remove. This application would be really beneficial.

You can use sandalwood with rose water as a treatment for dark underarms.

Wear simple cotton clothes especially in summers. This would reduce the chances of any infection.