4 glycolic acid hacks I swear by as a dermatologist. Glycolic acid is the ultimate multitasker because it’s an exfoliant, can remove excess oil, brighten skin & reduce skin pH to get rid of odor causing bacteria. Here’s how to use it: 1. For oily, greasy hair or treat a flaky scalp, apply glycolic acid directly to the scalp, leave on for 10 minutes and then shampoo as usual. Use 1-2x/week. 2. To help reduce back acne (bacne), put a spray cap on your glycolic acid for easy application and spritz