There are a lot of science-sounding skincare products we love using, but when asked to explain what they actually do, we’re sort of stumped. As far as we’re concerned, retinol definitely falls into that category. We know it’s supposed to be applied somewhere between our cleanser and moisturizer and that we should start using it in our 20s, but our knowledge of the fun facts stop there.

Perhaps the biggest conundrum is figuring out when to use retinol. Is it a morning or night product? Better yet, is it safe to wear in warm weather? Before summer officially arrives, we’ve got answers to these questions, and more.

What is retinol? What are its benefits?

Retinol sounds like a fancy ingredient, but it’s simply a form of Vitamin A, one of our favorite phytochemicals. It’s converted to the biologically active molecule retinoic acid once it interacts with skin.

There are a number of benefits to using retinol including enhanced collagen production, improved skin elasticity, improved skin texture, reduced acne breakouts, and decreased skin discoloration. Unless you’ve got a Vitamin A allergy, a retinol product should always be in your daily routine, along with an SPF moisturizer.

And although it’s often advertised as an “anti-ager,” those in their early-20s can benefit from it. Besides, if your goal is to delay the appearance of fine lines and wrinkles, getting an early start is better in the long run.

The differences between a retinol you’d buy in Sephora and one prescribed by a doctor lie more in the formulations and less in the percentage of retinoic acid in each one. Retinol is inherently difficult to keep stable in formulation. Whether a retinol product is purchased from a med spa or from a physician, the most important things to be aware of are stability and delivery technologies employed.

For instance, over-the-counter products usually include just esters—or compounds derived from retinoic acid—such as retinyl palmitate, retinyl acetate, and retinyl linoleate, which aren’t as potent. These are the ones that are typically referred to as “retinols.” It also will take slightly longer to see results from OTCs because they’re often mixed with other ingredients, as opposed to living alone.

On the other hand, prescription retinoic acid is more highly effective, because it isn’t diluted. However, its potency can be irritating to certain skin types. These are widely referred to as “retinoids.” You may have also heard of “Retin-A,” but this is simply a trade name for a specific retinoic acid, not a different molecule.

How do I use retinol?

The good news is that how you use retinol doesn’t have to change when the weather warms up. Regardless of the season, it should always be applied at night, although it also requires that you’re getting ample sun protection. The beneficial thinning of the stratum corneum that improves skin barrier and appearance also requires diligent sunscreen use. Because it’s thinning the skin’s barrier, you don’t need to use it every night, either.

Start by using the retinol two nights a week. As your skin adjusts to the use of the retinol, you will be able to slowly increase the frequency of application to nightly, or as many nights as are tolerated. And if possible, visit a dermatologist or skin health professional to discuss which retinol would be the most beneficial for you. The formula matters more than the texture, so there isn’t a specific form (serum, oil, lotion) you should be married to during the summer.

Whether you’re using an OTC or prescription retinol, make sure that your skin is well-hydrated and in proper condition to prevent skin irritation as it’s first introduced to the skin. Experts recommends mixing it with a moisturizer prior to applying both to the skin and using a night cream after.

Remember, retinol will help your skin with exfoliation and cell turnover, so you want to avoid combining it with other chemical exfoliants (AHAs and BHAs), as it makes it harder to convert retinol to retinoic acid and can disrupt the skin barrier, causing increased sensitivity and irritation. And since acids penetrate more easily when skin is at a lower pH, using a retinol right before or after could make them less effective.

The general rule of thumb: Stick to acids in the morning and retinols at night for best results, or if you’re more sensitive or outdoors more often, you can use your retinol and acids on opposite nights, avoid using either in the mornings.

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