Vitamin A aka Retinol

Retinol can be verry irritating to the skin, t is important to pick the right one for your skin type.

If your skin is ultra sensitive I recommend new retinol like products such as Embryolisse retinol like or Caudalie Resveratrol lift are a better alternative for sensitive skin as they are more effective than retinyl palmitate (it needs an extra step into the transformation and is less effective)

For normal skin I favor encapsulated retinol SVR fas a very concentrated serum called A ampoule
And if your skin is oily or acneic Face reality retinal B3 serum is the closest to retinoic acid with only one transformation step.