Are you using soap or shower soap for shaving?
If yes, replace this with shaving gel/cream/soap. Shower soap can be drying on the armpit area.
Dry skin will lead to inflammation, and inflammation will eventually darken the skin in the armpit area.
Is the blade in your shaver dull?
Dull blades can lead to ingrown hair, which in turn leads to inflammation in the armpit area, which in turn leads to dark armpits. Make sure the blade is sharp.
Are you leaving the shaver in the shower?
Don’t.
Leaving the shaver in the shower will make the blade dull.
Have you been using the same shaver for a long time?
Replace the shavers regularly.
Have you checked the ingredients?
Maybe the shaving gel/cream/soap contains ingredients like fragrance, denatured alcohol, or essential oils. These ingredients cause skin redness and inflammation, which eventually lead to pigmentation in the underarm area.
Did you exfoliate the previous day?
If yes, please don’t shave for 2 to 3 days after exfoliating. Exfoliating can be a bit harsh on the skin – and shaving is also a bit harsh. It is better to let the skin rest a bit after exfoliation. So avoid shaving for a couple of days after exfoliating.
Are you doing proper skin care after shaving?
After shaving, use skincare lotion or cream with calming ingredients in the armpit area. This will reduce inflammation.