Questions about actives

Plain answers, each with its sources. For two ingredients at a time, the ingredient checker answers from the same rules Corneo checks every routine against.

• Can you use adapalene with niacinamide?

  Yes. Niacinamide is not on Differin's avoid list, and it is well tolerated. How to layer the two, and what to keep off adapalene nights.

• Can you use azelaic acid with retinol?

  Yes. They do not conflict, and trials have paired azelaic acid with tretinoin. Both can sting early, so start them one at a time. How to fit them in.

• Can you use benzoyl peroxide with retinol?

  Yes, but not on the same night. Use them on different nights, or benzoyl peroxide in the morning and retinol at night. Here is why, with a schedule.

• Can you use niacinamide with retinol?

  Yes. Niacinamide is well tolerated and is often formulated with retinoids. How to layer the two, what studies found, and how Corneo schedules them.

• Can you use retinol and vitamin C together?

  Yes. The common split is vitamin C in the morning before sunscreen and retinol at night. Here is why, and how to set it up.

• Can you use retinol with AHA or BHA exfoliants?

  Usually not on the same night, and not while you start retinol. Why they conflict, what a study found, and a schedule that keeps them apart.

• Do vitamin C and niacinamide cancel each other out?

  No. The worry comes from lab tests in water from 1944 and 1963, not from skin. You can use vitamin C and niacinamide in the same routine. Here is why.

• Do you need sunscreen if you use retinol or acids?

  Yes, every morning, even if you only use them at night. What the AAD, the FDA and product labels say, what to look for and how much to use.

• How do you start an AHA or BHA without irritation?

  Pick one acid, patch test it and start at 2 nights a week. Corneo's schedule for an exfoliating acid, what to pair it with and when to step back.

• How do you start retinol? An 8-week schedule

  Corneo's own 8-week retinol schedule: 2 nights a week, then 3, then hold at 4. What the AAD advises, what to expect, and when to step down.

• How long until retinol shows results?

  Most sources point to 6 to 12 weeks for visible change, with dryness or flaking usually worst in the first weeks. What the studies and labels say.

• How often should you use retinol when you start?

  Start low and build up slowly. Corneo's own schedule is 2 nights a week for about 4 weeks, then 3, then 4, stepping up only when you did the nights.

• Moisturizer before or after retinol?

  Usually after: retinol on clean, dry skin, then moisturizer. Moisturizer first is an option for dry or easily irritated skin. What the sources say.

• Purging or irritation: how do you tell the difference?

  Purging looks like your usual breakouts in your usual spots. Irritation looks red, dry or flaky and stings. How to tell them apart and when to step down.

• Salicylic or glycolic acid: which one for your skin?

  Salicylic acid mixes with skin oils and reaches into pores. Glycolic acid works on the surface and raises sun sensitivity. How to pick one.

• Tretinoin and moisturizer: which goes first?

  The label default is tretinoin on clean, fully dry skin. Moisturizer first is an option to discuss with your prescriber. Here is what the sources say.

• Tretinoin vs retinol: what is the difference?

  Tretinoin is prescription retinoic acid. Retinol is sold over the counter and skin has to convert it first, so it is weaker and gentler.

• What does a skin barrier routine look like?

  Set strong actives aside, keep a gentle cleanser, a fragrance-free moisturizer and sunscreen, then bring actives back one at a time.

• What is skin cycling, and does it work?

  Skin cycling rotates an exfoliant night, a retinoid night and two recovery nights. No study has tested the cycle itself. What the evidence supports.

• What order do you apply skincare products?

  Cleanser, then the treatment, then moisturizer, with sunscreen last in the morning. The order for morning and night, and where retinol and acids go.

Corneo is not medical advice. If something stings, spreads or does not settle, talk to a clinician.