Because Kombucha tea adds a fermentation process to black tea the production and consumption of Kombucha tea can be dangerous. The majority of risks involved with Kombucha tea is contamination during the brewing process. Kombucha tea is highly acidic and can leach chemicals from the brewing equipment. To avoid this, brew Kombucha in glass, stainless steel or high density polyethylene (HDPE). In addition to this precaution, keep your utensils and brewing environment clean, keep your tea at the proper temperature and keep the pH low, between 2.5 and 4.6.
Kombucha tea in recorded history traces back to eastern Europe and Russia back to the late 19th century. The Kombucha culture looks similar to a mushroom but its actually a solid colony of yeast and bacteria added to black tea, sugar, brewed and allowed to ferment for seven to ten days. As Kombucha tea creates a new culture with each batch of tea it is feasibly possible to make a lifetime of Kombucha tea from a single culture.
The health benefits of Kombucha tea are so far based on personal accounts, laboratory testing and animal testing. There has been no clinical trial in humans to test the veracity of any of the health claims. On the flip side the most common dangers to consuming Kombucha tea include upset stomach and allergic reactions, as well as metabolic acidosis a condition in which the blood becomes too acidic.
In Iowa in 1995, the Centers for Disease Control (CDC) released the results of an investigation into two serious illnesses possibly linked to Kombucha tea, one patient who died. The two patients drank tea brewed from cultures that was linked to a common "parent" mushroom. One hundred fifteen other people drank tea from cultures derived from the same mushroom with no reported ill effects.
Because there is no clinical study on the effects, positive or otherwise, of Kombucha tea it is difficult to say that it is unnecessarily dangerous. If you decide to try Kombucha tea for yourself it is recommended to buy already brewed and ready to drink teas commercially available. If Kombucha tea is dangerous, it hasn't stopped other countries from consuming it for over two hundred years.
As with many other things, it's most important to keep everything completely sanitary if you're going to brew your own - but if you buy it commercially you're almost certain to be safe.