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.

The solution:

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.