Borax is a salt of the element boron. In its most common form, it is a chalky white crystal that contains a fair amount of water. It is also called sodium borate. A related compound, boric acid is created by the reaction of borax with strong acids. Borax has many uses in home products, manufacturing and industry. Borax is mildly toxic and while sometimes used in some Asian countries as a food tenderizer or curative agent, most western countries have banned its use in the food industries.

...
One of the most common uses for borax is in laundry detergents.

Ingestion

Ingestion of borax can be dangerous, especially to infants. Borax has been shown to be toxic to humans, and can cause nausea, diarrhea, vomiting and abdominal pain. In extreme cases, it can lead to severe rashes, loss of consciousness, slowed respiration and kidney failure. Other symptoms may include headache, weakness or convulsions.

Inhalation

Inhalation of borax powder can cause trouble breathing, coughing, sore throat and bleeding from the nose. Inhaling borax causes a shortness of breath; the victim may have difficulty taking deeper breaths without severe coughing fits.

Skin and Eye Irritation

Borax is an irritant. Contact with exposed skin can cause skin irritation, a red rash, pain and itching. Borax will also tend to dry out the skin, possibly causing cracking in extreme cases of prolonged exposure. Borax is very irritating to the eyes, causing a burning sensation, redness and eye pain.

Environmental Factors

Borox has been shown in many studies to be toxic to marine life; in higher concentrations it can be fatally toxic to fish, crustaceans, small worms and some types of plankton. It can affect the development of amphibians and some types of aquatic plants. Boric acid is sometimes used as a soil nutrient additive; care must be taken to monitor soil pH in these cases as it can raise pH levels and detrimentally affect acid-loving plants.