How to Lighten Dark Underarms

If however hair is not the problem the cause of dark underarms might be due to frequent use of some deodorants and antiperspirants.

Try to switch brands because some ingredients in the antiperspirants can also cause dark armpits.

The uric acid in the sweat can cause, over time, skin to darken.

Keep your underarms hairless or trimmed so sweat can not accumulate.
Apply talcum powder under your armpit that will absorb sweat making it less probable to cause dark skin.