cup of coffee
© Peter Dawson / RexA coffee can have consequences far beyond a caffeine high, if someone gets a sample of your DNA from the cup

When Ann Chamberlain-Gordon suspected that her husband was cheating, she took his underwear to her place of work - a police forensic lab in Lansing, Michigan.

Her husband, a former professional in the Canadian Football League, denied infidelity, but at a divorce hearing in March 2007, Chamberlain-Gordon testified that she had found female DNA on his underwear that did not match her own.

The opposing attorney quickly turned the tables on the forensic scientist, however, accusing her of misusing state equipment by running the tests. The Michigan State Police agreed, and Chamberlain-Gordon was fired a few months later.

If she had instead sent the underwear to a DNA testing company, such as Test Infidelity of Chatsworth, California, rather than taking matters into her own hands, Chamberlain-Gordon could have kept her job. "If you suspect your partner is being unfaithful, you can send in a pair of his or her underwear to test for the presence of another person's genetic material," Test Infidelity's website promises.

If Chamberlain-Gordon had suspected a particular woman and obtained her toothbrush, say, the company could also have analysed DNA from that to look for a match.

Test Infidelity is just one of dozens of US companies offering to test DNA taken without the knowledge of the people concerned. Many firms advertise infidelity testing services or offer "discreet" paternity tests. These allow a man to determine whether he is the father of a child without letting anyone else know what he is up to, or a woman to tell whether a man is the father of her child without involving him in the process.

While the total number of stealthy DNA tests being conducted is unclear, interviews with genetic testing companies indicate that thousands are being run each year in the US alone.

In the UK, such tests are already illegal. But though some US states have passed laws that arguably might outlaw aspects of infidelity or discreet paternity testing, extensive enquiries by New Scientist have uncovered no evidence that they have been used against firms running these tests.

This regulatory vacuum raises serious privacy issues, say legal experts. "Even if you are talking about someone engaged in behaviour that you may find dishonourable, this doesn't mean that person should be automatically stripped of all privacy," says Gail Javitt, law and policy director with the Genetics and Public Policy Center in Washington DC, part of Johns Hopkins University.

The results of paternity and infidelity tests can tear families apart. So firms that test DNA without consent could cause real harm - especially to vulnerable children. "The emotional consequences are not something that anybody is going to forget," says Denise Syndercombe-Court, who runs a DNA testing lab at Barts and The London School of Medicine and Dentistry. "Let's say a man wants to do these tests without the mother knowing. He's acting for himself; he's not acting for the child."

It is not even clear whether all of the firms offering stealthy DNA tests are delivering accurate results - so it is possible that some people's lives are being turned upside down by scientific errors (see "Beware the results").

We all continually shed cells into the environment, leaving our genetic calling card on items that can be picked up by others and analysed. Along with sources like semen stains, DNA can be extracted from such mundane items as coffee cups, chewing gum and even a well-worn hat. Some companies, including Genetic Testing Laboratories (GTL) of Las Cruces, New Mexico, provide a list of the various items they can process, quoting prices and the likelihood of getting a usable DNA sample for each.

DNA can be mined for deeply personal information, such as our susceptibility to various diseases. But companies like GTL and Test Infidelity are not offering to reveal people's medical secrets. Instead, they test for DNA sequences called short tandem repeats (STRs) which vary greatly from person to person and so are ideal for identifying individuals or determining whether two people are related.

Police scientists also use STRs, and TV crime dramas may have helped fuel demand for the technology. "CSI has gotten the public into doing these tests," suggests Barry Lenett of DNA Plus, Test Infidelity's parent company. "I think they do it because they can, and it's not that horribly expensive." To compare your own DNA with a stain from bedding or clothing, Test Infidelity charges $275. Matching DNA from the stain with that from an item used by a particular suspect costs another $175. Discreet paternity tests cost a similar amount: the DNA Identity Testing Center of Lewisville, Texas, charges $450 for a test involving one "forensic" sample.

With prices within the reach of many people's wallets, there is a steady demand. Vladimir Bolin, who heads Chromosomal Laboratories in Phoenix, Arizona, says his company processes around 1000 infidelity tests each year. "It's remarkably popular," he says.

Stealthy tests represent a small portion of the total genetic testing business, according to interviews with companies offering the tests. For example, Brandt Cassidy of DNA Solutions in Oklahoma City says that less than 5 per cent of the roughly 500 paternity tests run by his firm each year involve DNA from items such as chewing gum and drinking glasses. But with many firms offering these services, it seems that thousands of tests are run each year on the sly.

One place this should not be happening is the UK, where a pioneering law outlawing surreptitious testing came into effect more than two years ago (see "Celebrity concerns drive privacy law"). In most other countries, however, stealthy DNA testing has encountered few legal obstacles, despite the harm that could result.

"If everything we do is legal, I believe the people should be entitled to have what they want," argues Lenett of DNA Plus. "We don't get into the emotional aspect of it. That's for Jerry Springer. We just do the science."

In the US - the largest market for genetic tests - there is no federal law clarifying people's right to privacy with regard to "abandoned" DNA. So New Scientist teamed up with the Genetics and Public Policy Center to find out whether any laws in individual states might apply.

The resulting survey identified several states where collecting DNA samples for infidelity or discreet paternity testing, or running the tests themselves, could be judged illegal (see "DNA and the law"). But despite enquiries, including requests for relevant public records, New Scientist could find no sign that these laws had been used to crack down on companies running these tests, or individuals ordering them.

Even in New York, where the state's Department of Health does police companies to ensure they abide by regulations on genetic testing in general, there has been little action on stealthy testing.

Since 1996, it has been illegal to perform a genetic test on a resident of New York State, or to disclose its results, without consent. When the law was introduced, few people had heard of DNA testing for infidelity, or discreet paternity tests, and they are not mentioned specifically. But the law was drafted with a broad definition of genetic testing to allow for future developments. "We wanted it to be as encompassing as possible," says Ron Canestrari, now leader of the Democratic majority in the New York State Assembly, who sponsored the law.

In October 2007, the New York State Department of Health wrote to the paternity testing firm DNA Services of America in Lafayette, Louisiana, reminding it of the law requiring consent for genetic tests. In addition, documents obtained by New Scientist under the state's Freedom of Information Law show that over the past five years the department has written to more than 20 companies telling them that separate New York regulations demand that paternity or identity tests must be ordered by someone with legal authority, such as a doctor or a court official. This may have helped to prevent some stealthy tests.

Still, the department has issued no specific warnings about paternity or infidelity tests run on DNA taken from everyday items without consent. And New York's Office of the Attorney General, which would prosecute breaches of the 1996 law, has taken no action against companies running such tests.

In theory, a resident of New York or any other state with a relevant law who suspects that their DNA has been tested illegally could make an official complaint, prompting an investigation. Better still, Javitt argues that there should be a public debate on the ethics of stealthy DNA testing as well as legislation at the national level. "There should be clear boundaries on what is off-limits," she says.