There's nothing like being accused of ill-informed scaremongering (as I was in an irate comment posted the other day by a somewhat ironically named reader called 'Serenity') to send me foraging on the internet. I don't pretend to be well-informed, but I do take scaremongering seriously and try very hard not to, although willingly admit that I sometimes feel as though I am treading a fine line.

Serenity was reacting to a post in which I said that the preservative BHT is "used in embalming fluid, it was banned in baby foods by the FDA but is otherwise widely used in foods and cosmetics. It is banned in all food in the UK based on studies that it is carcinogenic (other studies suggest it might combat cancer - so at best BHT seems controversial)." Serenity countered that there is no evidence that BHT causes cancer. So I went back to my research drawing board.

Butylated hydroxytoulene has a remarkable research history. Since the 1970s, vast quantities of rodents have been sacrificed in the quest to decide whether it is friend or foe. This was - and still is - an important question; by the mid 1990s butylated hydroxytoulene was one of the (if not the most) common food and cosmetic preservatives in use. And some people started to get worried about it.

Business Week magazine in 1995 reported: "Several additives are suspected carcinogens. Take butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). Food companies use these similar chemical substances to prevent spoilage in foods with oil or shortening and to preserve many breakfast cereals (from Total to Quaker Instant Oatmeal), enriched rice products, and dried soups. Repeated studies have shown that BHA and BHT increase the risk of cancer as well as accumulate in body tissue, cause liver enlargement, and retard the rate of DNA synthesis and thus, cell development. However, one study, released in 1994, suggests these same additives may actually retard cancer development because of their antioxidant properties."

Business Week wasn't quite right. In turns out that there has been more than one study claiming that BHT retards cancer. I found two.

I have marshalled as much evidence as I practically can (the research archives are pretty extensive) and I think this is a fair representation of the for and against data. By the way, BHT has a close relative called BHA and many of the tests I found were conducted on both.

BHT prevents or retards cancer:

In 1999, a Taiwanese study claimed to be "the first demonstration that synthetic phenolic antioxidants decrease the N-acetylation of carcinogens and formation of DNA-carcinogen."

In 1991, GM Williams conducted a study and said: "These results suggest that the chemoprevention by BHT of cancer resulting from low-level long-term carcinogen exposure may be achieved at doses that do not produce adverse effects."

BHT prevents cancer but at the cost of causing it:

Not everyone agrees with Mr Williams. In 1996, the University of Hamburg in Germany examined the available published evidence and concluded that even though BHT can be anticarcinogenic, this is outweighed by its cancer causing tendencies:

"Specific toxic effects to the lung have been observed with BHT.... BHT induces liver tumours in long-term experiments. Because there is no indication of genotoxicity of BHT, all published findings agree with the fact that BHA and BHT are tumour promoters. In contrast to BHA and BHT, vitamin E is not carcinogenic. On the other hand, all three antioxidants have also anticarcinogenic properties. The intake of the necessary high doses as for these effects are, however, contraindicated with BHA and BHT because of their carcinogenic effects."

It is worth noting that the Hamburg team also thought that levels used in cosmetics were safe: "The present overview concludes that the concentrations of BHA and BHT nowadays used in food, drugs and cosmetics are probably harmless. In addition, vitamin E can also be used in higher doses without the occurrence of adverse effects."

BHT is carcinogenic, period

The number of studies showing that BHT is carcinogenic is impressive and I can only cite a few of them here. In high doses, BHT had a toxic effect on liver, lung, and kidney and also on the blood coagulation mechanism. It must be said, however, that all these tests seem have involved high doses of the stuff. For example, a 1988 study in Sweden on BHT and BHA concluded. "Both antioxidants were observed to be cytotoxic in a concentration-dependent manner at concentrations ranging from 100 to 750 microM."

A 2000 study said: "use of BHA as a chemopreventive agent against cancer in human has been challenged by the observation that BHA may exert toxic effect in some tissues of animals".

According to AM Malkinson of the Crisp Data Base National Institutes Of Health in 1999"...The food additive, butylated hydroxytoluene (BHT), encourages the development of tumors from previously initiated cells."

BHT is not carcinogenic

In 1979 study on rats was published by the National Institute for Cancer Research concluded that it is not carcinogenic. And GM Williams was sticking with his story in 2000 with a study for New York Medical College: "We conclude that BHA and BHT pose no cancer hazard and, to the contrary, may be anticarcinogenic at current levels of food additive use".

A Kuwait study found no evidence of carcinogenity but also that BHT isn't much fun for the liver: "BHT resulted in a significant increase in liver weight. The liver cells presented gradual vacuolization, cytoplasmic disintegration, "moth-eaten" appearance, ballooning degeneration, hepatocellular necrosis." A Swedish study also found that BHT damages the liver.

Most scientists tend to begin their reports noting that BHT is cancer causing. However, their studies then go on to show that the cancer causing effects are dose dependent. At low doses, BHT has been demonstrated to be safe. For example, A 1993 Japanese study was conducted on three generations of mice with BHT at 0.015%. "The dose levels of BHT in this study showed little adverse effect on reproductive and neurobehavioural parameters on mice.

BHT does not retard cancer

One of the most recent studies of BHT was conducted in 2006 in Argentina, expressly to test the theory that BHT retards cancer. The tests were conducted on hamsters and the researchers concluded that BHT did not stop cancer but in fact made it worse:

"Results obtained showed that BHT did not decrease the chromosomal damage induced by radiation in any consistent fashion. On the contrary, in cells post-treated with 5.0 µg/ml of BHT the yield of chromosomal aberrations increased in several experimental points."

In all the studies I consulted, BHT seems to have been administered orally. I didn't find any tests that have looked into its safety if used topically.