My skincare routine is excessively simple at this point in my life, which I am grateful for. While my morning routine involves splashing cool water on my face and moisturizing, my nighttime routine has always been a little bit more careful and deliberate; I consistently wash with a creamy cleanser that suits my dry skin and dab on whatever moisturizer I am fiddling with at the time, making sure to apply it evenly to both my face and neck. But the nighttime moisturizer is always more high end and contains better ingredients than my morning cream does. Why?  Because I have always believed that magical things can happen to my skin at night, if only I apply the right product. Yes, I said magical.

Doesn’t skin soak up ingredients more effectively at night than during the day? Isn’t there a reason that companies create separate night and day creams? Or is it true that your skin cannot differentiate between night and day, and cosmetic companies are not only in on that dirty little secret but also using it to their advantage? More products mean more money, after all. So the question is, do those serums and creams that promise to repair your skin while you sleep really work, and do they work differently from creams you wear during the day?

According to Kristine Cryer, vice president for product development at StriVectin, “At nighttime, skin does its repair. It’s not working hard like it’s working during the day.” Companies associate nighttime with renewal – and “regenerating, restoring and resurfacing,” all terms that imply that your skin is a “new blank canvas” come morning.

This might just be a clever marketing ploy, but it is actually true that the skin does go through some changes as night as you sleep. Its metabolic rate increases and “cells show increased production and a reduced breakdown of proteins,” which is all good news for those who desire beautiful, healthy skin. Also, blood flow seems to be higher at night and when blood flow is increased to the skin, the area of absorption (of whatever serum you put on at night) increases too.

Skin, like other organs, has a circadian clock. For example, our sleep patterns are linked to a circadian clock; in a roughly 24-hour period, we fall asleep at about the same time and wake up at about the same time everyday. Similarly, skin may actually be able to differentiate between night and day. There is evidence that points to skin cells following a circadian rhythm: the cells divide consistently in order to make up for dead ones.

Still, while there does seem to be a certain clock gene at work when it comes to our skin, the author of the study that found the gene says she does not “know whether the synchronization of clock genes may enhance the repair process of the skin.”

And as much as the skin does at night in order to repair itself naturally, there is no scientific evidence that the process that skin goes through at night is significantly different from what it goes through during the day. According to one dermatologist, “We are constantly repairing our skin and responding to stressors. Our skin doesn’t wait for nighttime repair.” In an interview with Cosmetics Magazine, Dr. Lisa Kellet, a dermatologist, says, “ Repair processes in the skin are an ongoing process occurring throughout the day. Otherwise, night shift workers would have a problem!”

There is no doubt that sleep itself is important for your skin’s health, but it has not been proven that using certain serums while you sleep increases their efficacy. However, there are some important reasons to use products with specific ingredients at night. For example, retinoids should always be used at night, as skin is more prone to burning when layered with retinoids and exposed to sunlight. In addition, certain ingredients tend to degrade when they are exposed to sunlight and may be most effective if used when it is dark. And if you are religious about applying sunscreen and makeup each day, it might be beneficial to use some anti aging serums at night when they won’t have to interact or compete with the other things you apply to your skin. These are all great reasons to use specific nighttime creams, but they really have little to do with sleep’s relation to the efficacy of products and more to do with lifestyle (what kinds of products you use) and sunlight exposure.