Kohl in Arabic is anything that is applied to the eye and/or its surroundings such as the eyelashes and eyebrows. Under this broader meaning, modern eyeliner and mascara products can also be regarded as kohl.
Given this, the answer to the question : Is kohl harmfull ?, is yes and no. It all depends on what it is made of.
People have used and still use different substances to adorn the eyes; essentially different types of kohl.
For example, frankincense resin was used in ancient egypt as a form of kohl. In India, many people who can not afford to buy commercially available kohl make their own one using soot and natural oils.
Even modern eye-makeup products, which can be regarded as kohl, can contain many harmful chemicals which are associated serious health problems.
Therefore, it is wrong to treat kohl products as one entity and then say it is harmful to health. Unfortunately, this is completely wrong approach is taken by the majority of scientific researchers who carried out research into kohl products.
Unsurprisingly, many of these research papers wrongly conclude that kohl is harmful to health because of it containing high levels of lead and other toxic material.
This is akin to saying that eyeliners and mascara are damaging to health. If this statement was to be made regarding eyeliner and mascara products, the first thing that comes to mind would be : which brands are to be avoided ? with so many different types of these stuff made from in so many different ways, surely not all of them can be the same.
Unfortunately, this simple common sense is missing when dealing with kohl products. They are treated as though they are one entity and the popular scientific opinion currently says : kohl is harmfull to your health.
The question is : which kohl ?
Ithmid kohl: Innocent till proven guilty
However, genuine Ithmid kohl is made only with 100% natural ingredient (s) and has no harmful side effects when used appropriately.
For over 15 centuries and counting, Ithmid kohl has kept its reputation as an effective and safe beauty and health maintenance substance, at least in the Arabian peninsula.
If it was harmful to health in any way, it is likely this practice will not have survived this long. But because it gives good results without any health problems, Ithmid kohl remained as a popular and sought-after substance.
Moreover, Ithmid kohl has been used and recommended by the prophet صلي الله عليه وسلم. Knowing this, a muslim should have no worries and anxiety about using Ithmid kohl. Rather than worrying about whether it is safe or not, our sole concern should be about obtaining genuine Ithmid kohl and avoiding the numerous counterfeit products out there.
There is no doubt that proper research into Ithmid kohl, which is completely absent, would have found it to be a truly wonder substance and that it poses no health risks whatsoever, when used appropriately.