"Very simply, lactic acid is a larger molecule, so it doesn’t sink in as deeply as glycolic acid ," said Riley. Typically, lactic acid is much gentler, but if those under-the-skin bumps just won't budge, it might pay to switch over to glycolic instead. And remember, it's all in the formulation. "If acids aren’t formulated well, they can really disrupt the moisture barrier of your skin, resulting in flaking and peeling," she continued. "Most acids are not in an emollient base, but the new Good Genes is in a slightly emollient base – not like Vaseline or petroleum jelly, but it helps protect the barrier of the skin. The glycolic acid is at 7% and the pH is 4.5. If an acidic product isn’t within an acidic pH [close to the skin’s pH of 5] then it isn’t going to work. This has the same backbone of how the original Good Genes is made, but it’s also cleaner for 2018, as we've changed the preservatives, while cactus extract reduces the stinging sensation. Someone with sensitive or acne-prone skin could just cleanse, put it on and then go to bed, no problem."