Glow sticks were the trickiest treat in this year’s Halloween bag.

The Rocky Mountain Poison and Drug Center received 43 phone calls on Halloween from people worried about children who had chewed on the neon tubes and swallowed some of the iridescent liquid inside.

A must-have for any Halloween costume, glow sticks make little goblins and ghouls more visible to cars while trick-or-treating.

Some, it seems, thought chewing on the sticks also was a good idea. Most calls involved children 18 months to 6 years old.

The foul-smelling liquid inside can cause skin irritation, itchy eyes and upset tummies, but not Halloween death.

Glow sticks contain two solutions. A small glass cylinder holds a hydrogen peroxide solution, which when broken combines with an alcohol mix, causing the stick to glow.

“While it is an irritant, it is not something you need to go to the emergency room for,” said Shireen Banerji, clinical toxicology coordinator for Poison Control.

The poison control center serves Colorado, Nevada, Idaho, Montana and Hawaii. Fourteen of the glow- stick calls came from Colorado.

While almost all the cases involved children — the youngest was a 10-month-old — the center did receive a call from one 45-year-old who had ingested glow-stick fluid, Banerji said.