Special Reports

JAPANESE wives are turning to off-the-shelf forensic science to catch their cheating husbands. Private detectives are selling them special chemical sprays that highlight telltale traces of semen in their spouse's underwear.

Called "S-check", the chemicals are supplied in two aerosol cans. Each of them is sprayed on the suspect underwear in turn. If traces of seminal fluid are present, the second spray turns it bright green. "I don't know if this is the same type of spray the police use," said a spokeswoman for the Gull Detective Agency in Tokyo. "I'm not allowed to tell you what the chemicals are."

But the method is believed to be similar to the most common test for detecting semen used by forensic scientists in Britain. Called the Acid Phosphatase Test, this also uses two chemicals. The first, alpha-naphthyl phosphate, is sprayed onto a blotting paper swab previously laid on the sample.

According to James Thorpe, director of the forensic science unit at Strathclyde University, Glasgow, the alpha-naphthyl phosphate reacts with the enzyme acid phosphatase in the semen to produce alpha-naphthol. That, in turn, reacts with the second chemical which is a dye. "We use a diazyl dye, which produces a bright purple stain," says Thorpe. "But you could get different colours by using different dyes."

The Japanese test relies on the fact that semen is secreted from the urinary tract for up to two hours after ejaculation. Takeshi Makino, president of Safety Tanteisha, a detective agency in Osaka, says the semen can be detected for up to two weeks if the underwear is not washed. He says his company is now selling 200 sets of S-check sprays every month—at Y35 000 (£175) each. Makino says this is a lot cheaper than the Y500 000 it costs to have a detective tail a suspected straying husband for a week. Of course, the test can also be done on women's underwear, but Makino says 99 per cent of his customers are married women.

Thorpe says that seminal staining on men's underwear is of no value as evidence to forensic scientists because acid phosphatase may be present from urination owing to leakage from the prostate into the urethra.

But semen detection is not the end of the story. The Gull Detective Agency says it has another weapon in its anti-adultery arsenal: a gel which a wife rubs discreetly on her husband's back before he goes to work.

If he has a shower during the day—seen as a telltale sign of an office affair in Japan—the gel reacts with water to form a blister which the wife can look out for when he undresses at night.

Gull says the same gel is also temperature sensitive. Rubbed into a man's socks, the gel will change the colour of the fabric if the socks are taken off for longer than 15 minutes. The agency would not reveal the composition of the blistering gel, saying only that it is called "infidelity detection cream".

The potential for catching innocent men in the adultery dragnet is all too real. As Thorpe says: "What happens if the man goes to the gym at lunch time? His socks change colour, his back blisters and his wife divorces him. Who said keeping fit was good for you?"