Armpits can become a real problem, especially because being a body area where you tend to sweat and is not as exposed to the action of air, tends to stain and also must add that some products such as deodorants and creams away from underarm stains out, tend to stain. It also happens with female shaving products.
When you shave your underarm area execute it with enough time to avoid having to submit to the rush, set aside time on weekends and is always day. Because after you dry shave and wash, wear clothing that allows free air circulation, it does not irritate and does not stain.
Avoid overly tight clothes or materials that are too hot, because that increases the sweat and dark clothing is a way to increase the problem of stained armpits, so cotton clothes and loose short sleeves prevent or slightly stained armpits.
And if you feel that your underarms look stained it is best to apply a little petroleum jelly under the armpits each night, after washing and drying properly, because that causes the skin to preserve moisture and will not smudge anymore.