In recent weeks, you’ve likely stumbled across a warning on your Facebook timeline: Don’t touch this caterpillar!

The critter in question is the hickory tussock moth caterpillar — hairy and white, with black spots down its back.

Most commonly seen in New Hampshire at the end of summer and early fall in nut-bearing trees, the caterpillars have been associated with rashes and allergic reactions, prompting parents to alert others to keep their children away.

But, the caterpillar isn’t harmful to all, according to Sam Jaffe, executive director of The Caterpillar Lab in Marlborough.

The worry stems from irritants on the caterpillar’s white hairs, which can cause allergic reactions when they come in contact with human skin, he explained.

Sometimes, people who touch the caterpillars develop slight redness on their skin or an itchy, burning rash.

“There are a ton of people that don’t get a rash from them,” Jaffe said, noting he’s one of them. “It’s hard to tell how people will react.”

Jaffe added that the hickory tussock — though booming in population in previous years — is relatively uncommon this year. More likely to find are the similar, yet less irritating, banded tussock moth caterpillars, which have yellow hairs.

But even when someone experiences a reaction from either furry insect, Jaffe said it’s extremely rare it will result in a serious medical issue.

Even still, area residents are wary.

Amy Blouin of Jaffrey is one of them. Her youngest daughter, Avery, 4, was playing outside at school a few weeks ago when a caterpillar fell out of a tree and down her sundress.

“She woke up the next morning, extremely itchy, and she was covered in a rash that went all the way down her back, across her stomach and down her legs,” Blouin said.

Avery was kept home from school and taken to the doctor, who Blouin said confirmed the caterpillar had caused the rash. She was given prescription-level hydrocortizone cream, and the rash subsided in about a week.

Blouin added she’s hesitant to have her kids play outside, with worries of the rash happening again.

Ashley Beckwith of Swanzey said her 2 year-old daughter, Emma, also had a run in with the caterpillar two weeks ago.

“We noticed that our daughter had broken out with a rash over her whole right inner arm,” Beckwith said in an email Tuesday.

Emma was brought to the emergency room, but Beckwith said the doctor didn’t know what caused the rash. When they returned home, though, she noticed the caterpillars all over their lawn.

Similar to Avery, Beckwith said Emma’s rash took a full week to vanish.

“We made sure she kept it clean, used Benadryl cream and had her wear long sleeves to distract her from looking at it to try to minimize the itching,” she said.

Others, like Tawnya Vigue of Antrim, said their children broke out in hives after time outdoors, but aren’t certain if the caterpillar was the culprit.

“[My son’s] doctor said she thinks it may have been from this,” Vigue wrote in an email Tuesday about her three-year-old, Logan. “We didn’t see him touch one, but we did go on a hike the day before and were looking at them all over the bridge where we walked.”

Jaffe said people shouldn’t panic when encountering the hickory tussock or any other hairy caterpillar, but use caution.

“The general rule is if they are hairy or spiney, don’t touch them,” he said.

Olivia Belanger can be reached at 352-1234, extension 1439, or Follow her on Twitter @OBelangerKS.