There are some dangers associated with a super-glue. Sticking things together which you didn’t mean to stick together being the obvious candidate. But apart from that, what most people are concerned about are cyanoacrylate and formaldehyde.
Cyanoacrylate is the main active ingredient of these eyelash extension glues. Wikipedia says that the UK’s Health and Safety Executive and the United States National Toxicology Program have both confirmed that the use of cyanoacrylate is safe. However, people can suffer effects from the fumes given off by the glue. Repeated exposure can cause flu-like symptoms in about 5% of people. It can also cause an allergic skin reaction is a small number of people, and trigger asthma in an even smaller number.
An allergic reaction can lead to the eyelids puffing up and becoming red and itchy. If that happens, then the eyelash extensions need to be removed. You should take a test for this by having what they call a ‘patch test’. This doesn’t really involve putting a patch on you, as the name implies. In fact quite the opposite. Although some professionals seem to think the way to test is to put a drop of the adhesive behind one of your ears, that is actually not recommended by manufacturers. The adhesive can always be an irritant on skin. For that reason when you’re eyelash extensions are attached, the technician is meant to ensure that the glue is at least 1 mm away from the base of your eyelash, so that it never actually touches skin. So the correct way to carry out a ‘patch test’ is in fact to attach two or three lashes to the outer edges of your eyes and then wait for 24 to 48 hours to make sure there’s no adverse reaction.
Allergic reactions are not considered to be particularly dangerous and will stop once the eyelash extensions and the glue attaching them have been removed from your natural lashes. The salon can easily do this. There are commercial products for removing eyelash extensions.
Apart from the cyanoacrylate in the glue, there is also a potential issue about formaldehyde. Formaldehyde can be emitted from glues if they are not properly purified or stored. Formaldehyde is not good for you. However, the amounts of formaldehyde that might be released are tiny.
The best protection you can have from any problems is that the area where the treatment is carried out should be properly ventilated.
One risk about cyanoacrylates: they can have an ‘exothermic reaction’ (otherwise known as going up in smoke) if they come into contact with cotton. So therapists do not wear cotton gloves or use lint when carrying out eyelash extensions.