Egypt
What: Milk baths

The history: Leave it to Cleopatra, in all her regal beauty, to soak in a decadent mixture of milk, honey, and essential oils. These luxurious baths were said to have given the Egyptian ruler radiant and supple skin. Today, milk baths are used mainly in spa environments, with refined, pasteurized milk infused with extracts and oils.

The lowdown: Because it's rich in lactic acid (which has an exfoliating effect), sulfur, calcium, and amino acids, milk is an ingredient used in many cosmetic cleansers and bathing products today, says King. However, don't expect the same benefits from drinking the stuff. "The downside is that digesting diary is now proven to cause acneic breakouts on the skin," she explains. "There’s a plus and a minus to everything."