Val Monroe
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A: Oils are generally occlusives, which means they help seal in moisture already in the skin, but they don't penetrate well, says Heidi Waldorf, MD, associate clinical professor of dermatology at the Mount Sinai School of Medicine. Creams and lotions, on the other hand, contain humectants that pull moisture from the environment and penetrate the skin's outer layer, plumping it; they also contain skin-softening emollients and occlusives.

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