On the one hand, preservatives aren't necessarily bad; their absence doesn't improve a moisturizer's efficiency in delivering beneficial ingredients to your skin, says Ni'Kita Wilson, vice president of Cosmetech Laboratories in Fairfield, New Jersey. On the other hand, some preservatives can cause irritation in sensitive skin, Wilson says. So if you tend toward sensitivity or you have skin allergies, a product without preservatives might be a good idea. As for freshness, mixing the ingredients at home and keeping the product in the fridge will prevent it from spoiling, but that won't make it more effective than a premade cream, says Kenneth Beer, MD, clinical instructor of dermatology at the University of Miami. I read Beer the ingredient list and asked him if there were advantages to preparing the cream at home. "Yes," he said. "You can probably fry garlic in it."