Some samples of granite have emitted levels of radon, an undetectable poisonous gas that can cause cancer. The concerns are strong enough to alarm many environmental scientists. However, other scientists do not believe that radon from granite poses a serious threat.
Radon results when natural deposits of uranium found in rock, soil and water decay. Therefore, at least trace amounts of this gas are found in most natural materials. Radon may enter homes from the soil below ground, which many scientists argue is more dangerous that the radon levels found in granite.
All unsealed granites are porous to some degree, meaning that they can absorb contaminants with which they come into contact. If you place raw food, especially meat, onto unsealed granite, it can become a breeding ground for germs and bacteria such as salmonella and e. coli. Do not place hot items on sealed granite, since heat can damage the seal and cause it to become permeated.
Granite is a solid composed of tiny crystals. This means that it is prone to cracking and chipping where the crystal bonds are weak. Not only are chipped areas of granite often sharp and dangerous for little (or even big) fingers and hands, but water can become trapped in cracks on a granite surface. Trapped water can cause mildew and a variety of molds, some of which are very dangerous to your health. Even if it remains undamaged, the crystalline structure of granite provides small niches that have a small chance of retaining moisture.
Just as granite may absorb germs and/or water, it can absorb other substances that will cause it to stain. Even richly colored foods, such as beets and greens, can release natural dyes that will leave their mark. The danger in this is especially apparent when working with non-edible substances on granite countertops. Glues, powders and many other items commonly used on a kitchen work area may be left behind to be transferred onto food items that are meant to be eaten.
Many cleansers can scratch or otherwise damage the surface of granite countertops, creating an environment that breeds the germs, bacteria and other dangers previously mentioned. Even those that do not mar granite may be soaked up by the porous material and can then be unintentionally ingested, causing illness.
While many dangers of granite countertops can be avoided by sealing them well once a year, if the seal is not done correctly it can actually pose a danger in itself. Sealant that is not applied in the right way may peel and end up in your food preparation, and if it is not allowed to dry thoroughly it can trap water beneath it that would otherwise have evaporated.