This is not an uncommon question and one you will see asked on many forums which is why I did we did YouTube video on it:
Eyelash Extensions burning suggest that the client is slightly sensitive to uncured adhesive vapours which can be released from the bonds when they get wet and this causes stinging.
Use a post bonder after the treatment, this will help quickly cure the bonds and seal them, it also assists with retention keeping the bonds elastic and flexible. We sell a super one called Rapid Cure.
You can also wash the lashes 5 mins after the treatment however this can reduce bond strength up to 30% so we don’t always advise although to do see this recommended on forums.
However, we instead suggest that after 12 hours (when the adhesive is cured enough: 90% cured) to get your clients to give their lashes a really good wash, washing away any vapours that are present and you’ll find this will solve this issue.