What it is:
Talc (also known as French chalk) is powdered hydrous magnesium silicate which sometimes contains a small amount of aluminium silicate.
What it does:
Talc is used to help control shine and absorb excess oil and moisture.
Talc also imparts stability, texture, water resistance and skin adhesion to cosmetics, and reduces the friction that can irritate skin.
It is also used in some cosmetic products like toothpaste, soap and detergents as a filler.
Talc is a drying ingredient and can, in some people, clog pores and cause breakouts.
Some people say that talc can cause cancer. The evidence that suggests talc can contribute to ovarian cancer is inconclusive. For more information, check out what The Beauty Brains wrote about the subject here.
There are also concerns that talc can cause lung cancer. To help prevent inhalation however, talc used in loose powder products in the USA is milled to a relatively large, non-respirable particle size (>5 µm).