Using deodorants or antiperspirants under the arms is one of the most common sources of cosmetic allergies. They can cause armpit itching when using deodorants as well as armpit rashes, peeling skin, etc. Because the ingredients in these products act as antibacterials to reduce bacterial growth, as well as perfumes to mask odors, armpit itching when using deodorants can occur as a symptom of irritation, especially on sensitive skin.