Each vial contains one 'serving' of serum, and although a bit of a pain to open, its a good system as you only use the amount of product you need to (I'm a bit of an over-user of products, so go through them quickly)
I did experience a tingle upon application, but nothing major and certainly not a reaction - just the chemical exfoliant doing its thing!
This kit is a fantastic system for exfoliating your skin gently over a week, leaving skin so much improved by the end of the 7 days. For me I found my skin was incredibly smooth and much more refined. My pores look smaller and the texture in general just looks more radiant and youthful.
A wonderful product to use, and one I'll happily recommend and use again. Thanks BR!