There could be danger lurking in that plastic pumpkin filled with Halloween candy. Doctors in Canada have found a biyearly spike in anaphylaxis, a dangerous allergic reaction, associated with Easter and Halloween.

It isn’t difficult to find peanut-based mini-sized candy at Halloween, from obvious ones like peanut butter cups and Snickers bars to more discrete cases, like some M&Ms or Butterfingers. According to a study published in the Canadian Medical Association Journal, researchers saw an 85% increase in anaphylaxis on Halloween and a 57% increase on Easter due to peanuts, an obvious allergen offender. General nut allergies, a response to unknown nuts, caused a 71% increase on Easter and a 66% increase on Halloween.

Most of the holiday cases of anaphylaxis occurred in children who did not have a known allergy.

The authors pointed out two big issues with the holidays. First, children often get candy from people they don’t know so well – or at all. Trick-or-treating, by definition, means requesting candy from neighbors, sometimes distant neighbors. Many of those giving out candy are not aware of each child’s allergies. Second, the smaller, “mini” or “fun-sized” candies given out at the holidays don’t always have the same level of allergen information that a full-sized product would have. In the case of mini candies, the allergen information might be on the bigger in-store packaging, but not on each individual wrapper.

Although the median age of the children in the study was 5 and a half years, more incidents were seen in children over 6. The researchers suggested this might be because older children are less closely supervised.

Families can set rules ahead of time or make a list of brands that are safe for a child with peanut allergies, such as fruit candies like Starburst, Skittles and Twizzlers. In extreme cases, parents can pack allergy-friendly snacks as a backup.

Knowing that serious allergic reactions spike at Halloween and Easter, parents and children should be encouraged to self-advocate and ask, “Does this have nuts?” For parents, it means the holidays can be a time of extra vigilance, keeping an eye on grabby hands and hungry mouths.