The skin under your arms is not that much different than skin on other areas of your body. Open pores can be the result of clogging. When oil builds up on the surface of skin, it collects debris and dead skin cells to form a plug. This plug settles into the opening of the pore and stretches it, making it appear larger and more noticeable. Pores don't really close, but when they enlarge they look like they are open. Developing a daily routine for skin care may be all it takes to close underarm pores.
Apply a mild cleanser to a cloth or your fingertips and wash the affected area twice a day. Pat dry with a clean towel. If the skin is irritated, avoid using fabric and just wash with your hands. Rinse thoroughly with clean water to remove any soap residue.
Exfoliate the skin once a week. Use an exfoliating product for delicate or sensitive skin. Follow the instructions provided with the product for proper use. This will help keep pores from clogging by removing dead skin.
Dab the area with an astringent at night only if there is no rash. An astringent will effectively clean the area and reduce pore clogging, but may be irritating to sensitive skin. Use the product lightly; do not over apply.
Skip shaving for a few days, especially if you have a rash. This will give skin time to heal and reduce the irritation.
Use an over-the-counter acne product for problems areas under your arms. This would be skin that develops blackheads or whiteheads. Apply the cream before putting on deodorant.
Use a deodorant that is for sensitive skin and scent-free. The problem under your arms might be an allergic reaction. Try rotating the deodorant you use until you find a product that does not irritate the skin and clog pores.