The pH scale (or potential hydrogen scale) is used to measure how acidic or basic a substance is and is rated from 0-14. Neutral substances will have a pH of 7 (think water). Anything with a pH below 7 is acidic (vinegar) and anything with a pH above 7 is basic (ammonia). Healthy skin has a pH of around 5.5, meaning that it is slightly acidic. If your skin is dry and sensitive, it’s likely that your skin is more basic (has a pH above 7). If your skin is breaking out and more irritated, it’s likely that your skin is more acidic.