“We asked them how they cleaned the pacifier — if they rinsed them in water — and of course most of them did,” Hesselmar says. But a lot of the parents did something else.

“They put it in their mouth, sucked on it and then gave it back to the children,” Hesselmar says. “It’s a quite common way to clean pacifier.”

When the researchers checked to see if there were any differences between the kids whose parents sucked their pacifiers clean and those who didn’t, they found there was. Those whose parents sucked the pacifiers clean were significantly less likely to have developed eczema at 18 and 36 months and less likely to have developed asthma at 18 months, the researchers say.

“Eczema is the best disease to choose [as a marker] if you want to see if a young child is becoming allergic,” Hesselmar says.