Factors That Increase the Risk. It can be caused by many factors. The fungus that causes thick yellow toenails is highly contagious; therefore, it is important to know what factors cause it to occur. Once you are familiar with the risks, you can then take precautions.
What is cornstarch? Cornstarch is a fine, powdery starch that is made out of corn. The cornstarch is actually made from the endosperm of the corn, which makes up most of the kernels that we eat when enjoying popcorn or corn on the cob. Cornstarch, also sometimes called cornflour, is produced by grinding, washing and drying the endosperm of the corn until it reaches that fine, powdery state. Cornstarch is gluten free. Cornstarch has many culinary uses, but it is most often used as a thickener for sauces, gravies and fruit pie fillings. Cornstarch thickens very quickly and easily, and forms a clear sauce after cooking, rather than an opaque one.
This is paraphrased from Wikipedia. Corn starch a fine, white powder processed from the endosperm (the starchy part, ie, not the hull or the germ) of corn or maize grain. It is used as a thickening agent. I use it in gravy and for custards. It is also added to other products like powdered sugar and talcum powder as an anti-clumping agent.