NEW YORK (CBSNewYork) — Millions of people think they’r allergic to life-saving medications like penicillin, but a recent study found that 90 percent of those folks aren’t allergic to the drug at all.

They may be reacting to some of the inactive ingredients in the pills. Those can be dyes that give pills their different colors, or maybe the binders and fillers that hold the pills together. All those things play an important roll in drugs, but they can cause allergies and often they’re not listed on the label.

Medications come in such a wide variety of shapes, sizes, and colors that even Halloween candy can’t match. But all those colors and types of pills can come with a hidden risk.

“There are a lot of people that are allergic to preservatives or artificial dyes, or binders that are used in medications,” Dr. Purvi Parikh from the Allergy and Asthma Network said. “It’s not really the medication itself.”

It’s what plagued Sigal Hurvitz Bin and her daughter. They would take medicine and both would have a similar bad reaction,initially thinking that they were having a frightening allergic reaction to the drug they took.

“My lips will swell, my tongue will swell, I’ll start losing my voice which is an indication of throat swelling, which again can lead to anaphylaxis,” she said.

As it turns out, Sigal and her daughter both have severe gluten sensitivity. Gluten is used in many medications as a binder. Her daughter is also allergic to one of the dyes used to color many pills.

Both are important components of drugs which stabilize, preserve, and aid with time release of active ingredients. Color helps distinguish between different drugs and different strengths.

“The tell-tale sign is if someone is allergic to seven or eight seemingly unrelated medications, it probably isn’t that they have that many allergies,” Dr. Parikh said. “There’s one common agent tying it all together. It could be a dye or a preservative or a filler.”

The problem is that most medications, both prescription and over the counter, aren’t required to list those inactive ingredients. It’s something Sigal says she’d like to see changed.

There are several good allergy tests for the ingredients, but it’s left to the doctor to figure it out with careful detective work.