I really love this toner and serum. The serum does not sting if my skin's barrier is okay. I did notice that when my skin had a bit of a rough patch (I was too sick with flu to bother with a full skincare routine) that it did sting a bit. However, when my skin condition improved, it no longer stung. I even bought some to gift to my sister. She loves it, too.
It didn't stink on my skin like others experienced. But my face definitely becomes smoother only after 3 days of application of the serum. Highly recommended.