It might not surprise you that Halloween is the US's no. 1 candy-selling holiday, but what may come as a shock is the amount of money Americans are expected to spend on candy this year. Here's a hint: It's in the billions.

According to a National Retail Federation's consumer survey, trick-or-treaters can expect to carry home up to $3.5 billion worth of Halloween candy this year. Anyone who participates in the holiday knows that, despite how many sweets you or your kids can eat in one night, the candy we stock up on during trick-or-treating and Halloween parties can often stretch a long way. 

If you've ever opened your pantry months after Halloween and wondered if the candy is still safe to eat, the simple answer is that it's probably completely fine. But when it comes to candy expiration dates, it's a bit more complicated than that. So we spoke with an expert to learn everything there is to know about the shelf life of candy as America's most confection-heavy season approaches.

Does candy expire?

Yes, but not in the same way that perishable items such as eggs, chicken and produce do. When candy goes bad, it's "almost always a physical (drying out) or chemical (lipid oxidation, flavor change) change and not microbial," Richard W. Hartel, a food science professor at the University of Wisconsin-Madison, says. 

This means that, while candy does technically expire, it's quite unlikely that it will make you sick if you indulge in a few pieces of candy that have surpassed its best-by date.

"Eating old candy may not be the most pleasant experience, but by and large won't cause any adverse health effects," Hartel, who's also the editor-in-chief of IFT's Journal of Food Science says.

Do different types of candy last longer than other types?

Yes, but it depends largely on how each type of candy is stored. While chocolate is shelf-stable for about a year if it's stored at a cool temperature with low humidity, according to Hartel, hard candy can last much longer. 

"Hard candy, as long as it's protected from heat and humidity, can last several years with little to no change," Hartel says. 

However, if hard candy is "exposed to warm temperatures and high humidity, it picks up moisture from the air," he adds. "This can cause a variety of changes, from stickiness to crystallization and flavor loss, depending on the formulation."

Chocolate should typically be stored at cool temperatures and can be frozen. When chocolate ages, it may start to appear dusty. This is known as chocolate blooming.

"This is not a microbial growth, but simply a recrystallization of the cocoa butter on the surface of the chocolate," Hartel says. "It's mostly a visual issue, although excessive bloom will also adversely affect flavor release and enjoyment. Again, bloomed chocolate is not unsafe to eat, it's just that the chocolate won't be as delicious as it initially was." 

Should you throw away old Halloween candy?

Not necessarily. This is more of a personal choice than a health concern and answers vary from person to person. It's up to you to decide if your candy corn or caramel is too hard to eat, or if the coating on that chocolate makes it no longer appealing to you. 

"Different people have different thresholds, but several months would generally be fine," Hartel says.

How to store candy

To keep your candy at its peak flavor, don't store it in a high humidity or hot temperature area. 

"For most candies, cool temperatures and moderate humidities work best," Hartel says. "If humidity is too high, the candy might pick up moisture and get sticky, but if too dry, the candy will lose moisture and harden quickly."