TORONTO - For those who are worried about warts, a new study from the Netherlands might help with the decision about how to treat them, or whether treatment is even worthwhile.

Warts that had been around longer -- for more than six months -- were less likely to be cured by treatments, the study found. And it identified important differences in the response to treatment for plantar warts on the soles of the feet and for common warts, found on the hands and other parts of the body.

In the study, published Monday in the Canadian Medical Association Journal, the most effective treatment for common warts was cryotherapy, using liquid nitrogen applied by a doctor every two weeks. Forty-nine per cent of patients in that group were cured after 13 weeks.

By comparison, the cure rate was only 15 per cent for patients in a group self-treated daily with petroleum jelly that contained 40 per cent salicylic acid -- a higher concentration than is found in over-the-counter products in Canada.

Warts were gone after 13 weeks for eight per cent of those in a control group that did nothing and took a wait-and-see approach.

Among children under 12, more than half of patients with plantar warts were cured in the groups treated with liquid nitrogen or salicylic acid, while 43 per cent in the control group had their plantar warts go away even if they did nothing.

But the outcome was dismal for teens and adults with warts on the soles of the feet. Cure rates did not differ significantly between treatment groups -- only about five per cent had their warts go away.

"If anything, it was a bit disheartening to see that they've proven that liquid nitrogen doesn't work for plantar warts, the problem being that well then, what do you do? So people wait six months to see me -- usually they aren't thrilled if I just say, 'Oh well, just wait,"' said Dr. Peter Vignjevic, an assistant professor at McMaster University in Hamilton and a practising dermatologist.

"And they'll say 'Well, I've been waiting a year or two.' Then I'll say 'Well, wait a few more years.' That's not what they want to hear."

Vignjevic said he probably sees 60 to 70 people a week with warts, which are caused by human papillomavirus.

He observed that the Ontario health insurance plan provides coverage for treatment of plantar warts, which doesn't seem to work, while it does not pay for treating common warts, which is more successful.

"It doesn't make a lot of sense to me."

But timing may be everything.

Dr. Jason Rivers, a clinical professor at the University of British Columbia, said it's interesting that the study found people who had warts for more than six months, regardless of the type of wart, had a poorer response than those who had them for a shorter period of time.

This may suggest a change to the wart virus itself, in that it's becoming more incorporated into the body's system compared to a newcomer that may not be as established and able to defend itself, he speculated.

"I think this study does suggest that treating warts earlier is better than treating a wart later," he said. "If you look at cryotherapy for common wart, it's 83 per cent success rate if the wart was there less than six months, and it dropped down to 33 per cent for more than six months."

"Plantar warts, regardless of what you do, seem to be more difficult to deal with. Again, though, there was a 50 per cent response rate with cryotherapy if they were less than six months, but it dropped down to 11 per cent if they were there more than six months."

Rivers said there are more than 100 different wart viruses, and they have different predilections for attaching themselves to skin. Plantar wart viruses are able to deal with the thick calloused skin on the sole of the foot, he noted.

In reviewing the study, Rivers also noticed that the results tables didn't give a breakdown on the basis of number of warts. If people with more warts by chance ended up in the wait-and-see group, then it could make a difference, he said.

The randomized controlled study involved 240 people aged four to 79 in the Netherlands who showed up at 30 family practices for treatment of warts.

Co-author Dr. Sjoerd Bruggink of Leiden University Medical Centre said 90 per cent of people get warts during their lifetime, and it's one of many minor ailments seen by family physicians that is understudied.

"There's not much money to finance such studies, so I think it's very important," he said in a telephone interview.

"They're totally harmless but they can be very annoying," he said. "We did another study in which, in primary schools, one-third of children had warts somewhere. So it's a very common problem. They ... can also irritate on the feet or on hands. So it's harmless, but annoying."

Vignjevic agreed that warts are not dangerous, although warts on the cervix can predispose a person to cervical cancer.

He also noted there can be side-effects to cryotherapy. It can be painful, cause redness, swelling, blisters, some scarring and residual increased or decreased pigmentation that's sometimes permanent.