Can I use retinaldehyde (retinal) together with niacinamide?

Yes — these two are compatible and often used together. Retinaldehyde is a vitamin A form (retinoid) that can bring a short adjustment period of mild dryness or flaking as skin gets used to it. Niacinamide supports the skin's own barrier lipids (it encourages ceramide production) and has a calming, anti-redness quality, so using it alongside retinaldehyde may help ease that adjustment and keep skin feeling more comfortable. A common approach is to lean on niacinamide for barrier support and retinaldehyde for its renewing, smoothing role — introducing the retinoid gradually, and patch-testing first if your skin is easily reactive. This is cosmetic reference information, not medical advice. The concentration that matters is in the app.