Why Do I Get Bumps Under My Armpit?

The deodorant you use is cloging your pores which causes you to have ingrown hairs. Switch to a deodorant that does not have antiperspirant in it.

There are too many different things that it could be, but the immediate thing that comes to mind is to change the brand of deodorant that you are using.
Wait a little while before you apply it after showering, whether male or female, it doesn't matter. If this continues, take a look at the ingredients that are going into the deodorant, and compare the other brands, maybe you just have sensitive skin, and you might use a deodorant that is organic, that might do it for you. Hope this helps, good luck.

Shaving with warm water and then applying deodorant will cause this to happen. Always rinse your shave blade with cool not hot water, and wait a few minutes until skin is dry before applying deodorant. Also change directions to shave in the direction hair is growing.

Could from your deodorant or it's just an ingrown hair so try using Nair and see if that helps.

It is most likely razor burn try after shave gel should stop th bumps and pain.

One reasoin could be mainly because you may need to change the deodorant brand. It also cause irritation in your skin just like a rash which may spread and cause you to scratch, making the pain hurt.

The Bumps are caused by irritation or sensitivity to the deodorant you are using. It can also be caused by the trauma/irritation from shaving [if you shave your underarm].

You can quickly get rid of the bumps using the New BUMP ZAPPER Anti Bump Healing & Skin Repair Lotion.

It is available at Rite Aid Pharmacy or online at
www.bumpzapperforwomen.com

If you are female and have just shaved I would wait 30 minutes and then try putting on your deodorant. Have you changed deodorants?

If you are female probably due to shaving then applying deodorant, typical.
If male perhaps you are allergic.