Blackheads under the arms are the same as those on any part of your body. Hair follicles produce oil that helps to protect skin. When the follicle becomes clogged, oil builds up and skin becomes irritated. Clogged pores that remain open at the surface have a black appearance. Shaving and sweating are enough to irritate the skin under your arms. This irritation blocks the pores, and you develop acne. For mild acne, treatment can include some basic hygiene and over-the-counter medications.
Wash under your arms at least twice a day with a washcloth and mild cleanser. Clean the area well after exercising.
Apply an over-the-counter ointment under your arms at night. Select a product containing benzoyl peroxide or salicylic acid. If the cream causes more irritation, discontinue use.
Use a hypoallergenic deodorant. Any type of irritation can lead to clogged pores and blackheads, and this includes dermatitis from deodorant. If the blackheads increase with a particular type of product, change until you find one better tolerated by your skin.
Put a hypoallergenic body powder under your arms to absorb oil. Overproduction of oil can cause clogs in pores. Powder under the arms will absorb the oil and should reduce problems.
Apply shaving cream under your arms before using a razor. Use the cream liberally. Shave with a single-bladed, disposable razor, and change the razor each time. Double-bladed razors damage the surface layer of skin and can lead to blackheads.