They found several creams caused skin cancer in the specially bred mice, which had been pre-treated with ultraviolet radiation. The cancers are not melanoma, the deadliest kind of skin cancer, they stressed in their report in the Journal of Investigative Dermatology, but another type called squamous cell carcinoma. Such tumours are slow growing, highly treatable and only fatal if patients fail to have them removed. Allan Conney and colleagues at Rutgers University in New Jersey said they discovered the risk while testing a theory that caffeine could prevent skin cancer. “We sort of got into this by accident,” Conney said in a telephone interview. “We wanted a safe cream that we could put the caffeine into.”   They were testing specially bred albino mice, which are prone to develop skin cancer. The mice are pre-treated with ultraviolet radiation to simulate the effects of a human who has had heavy sun exposure in the past but then stopped — something that may be happening in the population as people realize the risks of getting a tan. Conney’s team decided to test the creams first and found that all four they tested caused tumours to grow on the mice. He said he does not know why, but suspects two ingredients — mineral oil and sodium laurel sulphate. “We’d like to understand the mechanism. What is most important is to see whether these moisturizing creams are tumorigenic in people,” Conney said. He said his lab is not equipped to do this but someone should. But he added, “I don’t think that people should be scared because this is a mouse study and we don’t know whether or not it applies to humans.”   Other experts were sceptical about the study. “This is a pretty artificial situation with the mouse skin primed by a lot of UV light to develop cancer,” Karol Sikora, Medical Director of Cancer Partners U.K. in Britain, said in a statement. Dr. Jonathan Rees, an expert in dermatology at the University of Edinburgh in Scotland, said squamous cell carcinoma was not a big health worry. “Non-melanoma skin cancer in man is very, very common and is almost 100 percent curable with an operation usually simpler than a tooth filling,” Rees said in a statement. Conney said the mouse was a commonly used model in skin cancer but said he agreed that it does not perfectly replicate human skin and human behaviour. He said his team approached Johnson & Johnson to create a cream without the suspect products and they developed one using other readily available ingredients. “They are things that are commonly used in many moisturizing creams,” he said. This cream did not cause the tumours in the mice, they said. He said Rutgers and Johnson & Johnson had patented the new cream jointly but did not know whether it would be commercially developed. A spokesman at the company was not immediately available for comment.
Skin creams seen to cause tumours on mice.