I use it 2-3 times per week at night and so far it hasn't irritated my skin and I can see my acne scars slightly getting better (2 weeks of use) which is why I'll give it 3 stars for now. When I first used it, I had a slight reaction but that's because I used it with an exfoiliating product that also contained niacinamide so be careful not to use products with high % of niacinamide with this serum at the same time. I will continue to use it.