Yes, they are dangerous. The materials of novelty contact lenses have not good oxygen permeability. If you wear it for a long time, you eyes will feel painful and itchy. And if you have eye problems such as myopic eye, strabismus, wearing novelty contact lenses will lead to many eye diseases, because it makes cornea thinner.
Novelty contact lenses are lenses printed with various designs. Because these kind of exaggerate design, the novelty contract lenses will make it easy to transform your appearance. They become a very popular trend in parties. However, you should know the risks of novelty contact lenses. Actually, it has found that in many places there are people getting infections caused by this kind of lenses, some people even become blind. If you really want to buy a pair of novelty contact lenses, you should go to an ophthalmologist to check your eyes are fit to the lenses. After you get the lenses, you should try to keep them clean and reduce the time of wearing them. I think it will be no big deal to just wear them occasionally.
Yes, your mother is right on wearing unqualified contacts is dangerous. For example, these contacts may make your eye field narrower as they focus on the effect of making your eyes look big but reduce the area of the middle. The contact lenses could be so bad that color your eyeballs as the pigmentary layer contact with your eyes directly. If you enjoy the parties so much that you forget to get them out from your eyes when you drinks much, you eyes may be lack of oxygen and you may suffer from dry eyes. So, if you want to buy some contact lenses which are very attractive, you should make sure they are in high quality.
I didn't try the novelty contact lens yet, but I can give you some information about it. The novelty contact lens is also called cosmetic lens or Plano lens. It's a fashion item that made by soft plastic to change the appearance of eyes, especially enhance the beauty of the eye. Unlike the corrective contact lens, it could decorate the eye instead of change the eye vision. That is to say, it's not safe to wear the novelty contact lens frequently in daily life. However, you could wear this kind of contact lens with risks. Firstly, there are various colors of novelty contact lens are available, thus it would block vision if the design is less transparent. And it would irritate your eyes when inserting the contact lens at the first time. It takes a certain period to adapt it by your eyes. On the other hand, it's not suitable for daily usage that not recommended by the eye doctor. And like other contact lenses, sleeping in novelty lenses is a serious risk of safety. It would cause damage of the eyes if the user couldnâ€™t follow the proper contact care.