The above advice if it’s boils. But honestly it looks like friction irritation and jock itch type fungus. For fungus just bathe often, use antibacterial wipes or alcohol and secret unscented antiperspirant. Wear soft t- shirts to keep friction and moisture wicked away even while sleep. Do not wear synthetics. If I sleep shirtless, sweat will cause fungus in my pits. Also honey kills fungus if help it on there but the stickiness will drive ya crazy and u can’t leave the house with it on. Too messy.

I've used honey and it is amazing, but messy for sure. I have used it with bandaging!

hot tub soaks hot as can stand it 3x day. Can put wet wash cloth then plastic wrap, then a towel over that then a heating pad over that as a wet warm compress. If it develops pus draw it out with ichthomol black drawing salve. After bath use equate red top antibacterial wipes or alcohol to kill any trace of staph BO. Then apply secret fragrance free antiperspirant spray. Don’t use roll on or solid as it will continually reinfect you. Some people afraid to used antiperspirant but antiperspirant kills germs and prevent growth. It doesn’t look like your bumps have pus. It looks like friction caused inflammation. Did u exercise with lots of arm movement or do a chlorinated pool aerobic workout? I get this in chlorinated pools cuz it dries my armpits and kills my skin natural flora and causes boils.

I am not a doctor but that redness isn’t good, u should maybe see a doctor love