This can happen especially in winter due to the heating which makes the air dryer. Fumes from the glue are attracted to humidity and when the room is dry, it goes for the eyes, nose, mouth and can create irritation. We recommend the use of a humidifier in winter to counteract this. Another reason could be if your clients eyes were half open during the treatment, fumes easily went in to the eyes. In this case your client can get chemical burn- red line, which can be mixed with allergy. Make sure your clients eyes shut properly. Being a lash artist it is not easy, clients always think that they reacted to the glue, but this is not the case. Sometimes they can react to cleanser, for example, eye pads etc Always read ingredients which listed on the product, your client may be allergic to one of them. Even if you did everything correct, your clients may develop sensitivity / allergy, as we using chemicals. Direct them to see the doctor.