Be a Sensitive Shaver
Shaving can be rough on sensitive underarm skin. Make sure that you use products free of common allergens and irritants, and that also help retain the skin's moisture levels.
You don't need to use a special shaving gel or cream for your underarms -- but avoid using soaps that contain deodorants, fragrances, alcohol or other ingredients that can dry out and irritate sensitive skin. Whether you use regular body soap or a special shaving gel, choose mild products that contain moisturizers.
This may sound obvious, but you should make sure that you use a new, sharp razor when you shave. Of course, you should use your own razor when you do so; shared razors spread bacteria. Don't push down too hard, either, because the blade can push bacteria into your hair follicles and cause infection [source: Monroe].
One of the best ways to be sensitive to your underarm skin is to shave less often. If you allow more time for the hair underneath your arms to grow, the skin there will retain more natural moisture and be less prone to irritation. That said, allowing your armpit hair to grow may be a luxury you can't afford during beach season.