I find patch testing an interesting topic when it comes to eyelash extensions. The glue used for this treatment should NEVER, EVER touch the skin. It is not designed for skin application and the manufacturers, well mine at least, always advise not to place the glue on the skin. Therefore patch testing the glue on the skin IMO should never be done, although I am aware of lash companies insisting on doing this.
Allergies are 'buggers' as it really is impossible to advise whether a new client, or existing one, will react to the products, although the technician could have indicators, such as plaster allergies, but it doesn't guarantee the client will react to the glues. Reactions are usually from the fumes the glue generates when it starts to oxidise, ie become sticky, which is an essential component of the product. The client will either be allergic to the Acrylic or the Formaldehyde that ALL eyelash extension glues contain. Common Complaints: Swollen eyelids, itchy and irritable eyes.
My advice would be to offer a free removal if the client does develop an allergy. In all the years I've been doing this I've only ever had to remove 3 sets and I have a few clients who have an allergy but still continue with this treatment as the affects die down, anything from 24 hrs to a couple of days.
Hope that helps.
Francesca
Trainer and Master Technician in Individual Eyelash Extensions
LASH by Francesca