Looking for love? Try leaning in for a ... cheek swab.
A couple of genetic testing companies are promising to match couples based on the DNA testing, touting the benefits of biological compatibility.
The companies claim that a better biological match will mean better sex, less cheating, longer-lasting love and perhaps even healthier children.
"How many dating services can you think of where they can suggest you might have better children?" said Eric Holzle, founder of ScientificMatch.com, one of the first online dating sites to use DNA.
Holzle wouldn't reveal membership numbers, but GenePartner, a Swiss company that works with matchmakers and dating sites, has tested more than 1,000 people, according to chief scientific officer Tamara Brown. Some were already coupled and took the test out of curiosity.
The GenePartner Test is $99, and will be offered at the dating site sense2love.com when it relaunches next month.
The idea is that people tend to be attracted to those who have immune system genes that are dissimilar from their own.
Biologists say the HLA genes of the immune system _ which are responsible for recognizing and marking foreign cells such as viruses so other parts of the immune system can attack them _ also determine body odor "fingerprints." And people tend to be attracted to the natural body odors of those who have different HLA genes from their own.
In one study, Swiss biologist Claus Wedekind found that women who were not taking hormonal contraception preferred the natural scent of men whose immune systems were the most different from theirs.
But don't put too much faith in this, experts said.
Dr. Rocio Moran, medical director of the General Genetics Clinic at the Cleveland Clinic, called the idea "ridiculous," and said the science of attraction is too complex to look at only a few genes.
"They are just trying to make a buck," she said. "That if it's genetic, it must be real science."
When a random sample of married people was studied, their immune systems were not that different, said Patrick Markey, associate professor of psychology at Villanova. And he notes that hundreds of studies have shown the importance of personality and physical appearance in choosing a mate.
For some, factors such as whether the person smokes, is fat or wants children will override biological compatibility, said Helen Fisher, a biological anthropologist and author of "Why Him? Why Her?" She believes genes play a role but said it's only one part of the puzzle.
Rachel Herz, author of "The Scent of Desire," who teaches olfaction and human behavior at Brown, believes the science is legit but thinks prospective matches should swap T-shirts and sniff.
"Above all physical factors _ for example, how he looks _ and social factors, how guys smell is more important than anything else," she said.
Holzle was not able to point to any success stories. He said his site tends to attract people who are concerned about privacy and has not done a good job tracking members once they leave. GenePartner did not respond to a request to speak to its customers.
But Chris Moyer, 57, a computer programmer in Reading, Pa., said she would be willing to try it. She has used four or five online dating sites.
"When eHarmony failed, I just gave up," she said. "Nothing has worked, and I'm curious to see how this would work."
Singles who sign up for ScientificMatch.com get a welcome box in the mail containing a skin cells-swab kit. The person mails the kit to the lab, with results in approximately two weeks, then uploads a profile and photos and takes a personal values test. The site also conducts a background check.
Matches are generated based on the DNA, values and preferences.
But Holzle didn't have any success stories to share. In fact, he is planning to phase out the dating part of the site he started in 2007 to market the tests directly to matchmakers and couples. He promises a refund of the $995 lifetime membership.
Still, some matchmaking services are willing to incorporate the test to help frustrated clients.
Anju Rupal, founder of sense2love.com, a Switzerland-based matchmaking site for English speakers, including members in the U.S., is partnering with GenePartner. Members are not required to take the test to sign up, but are encouraged to do so to whittle down the number of potential matches.
"A woman wants to date, settle down and have children. Guys don't want to waste time," she said. "Our aim is to do the best possible match in the shortest amount of time."