The deciphering of the human genome has prompted a number of entrepreneurs to cash in on people’s genetic concerns. They offer DNA testing to look for aberrant genes associated with the risk of developing various diseases, especially cancer.

Such testing, when done reliably, might encourage some people to take charge of their health and make better plans for the future. But some professional genetics counselors say this approach to determining cancer risk is fraught with hazards, not the least of which is a false warning of a serious risk that does not exist.

“This kind of testing is premature,” said Dr. Kenneth Offit, chief of clinical genetics at Memorial Sloan-Kettering Cancer Center. “Some companies are selling research tests for mutations that carry a low risk of causing cancer, leading people to worry needlessly or be falsely reassured.”

Another problem, he said, is the prescription offered after the tests.

“Other companies are telling people what kind of foods to eat and what to put on their skin based on their genes,” Dr. Offit said. “Testing for known cancer genes is legitimate, but often the prescription given for a ‘gene makeover’ is not. Regulation of these labs is sorely needed. And people facing real hereditary cancer risks require intensive professional counseling.