Expired soap may still protect you against harmful germs — here's how to tell if your expired soap is effective

• Soap does expire, but if it still lathers when you wash your hands, it should be effective.
• Most commercial store-bought soaps expire after two to three years.
• Natural or handmade soaps may expire sooner, within one year, as the essential oils and fragrances can get rancid or moldy.

Most soaps are regulated by the Food and Drug Administration (FDA), which requires all drugs to have expiration dates. That's why you'll see an expiration date on bar and liquid soap.

While most manufactured brands can last up to two years or longer, some handmade soap makers recommend using their soaps within a year of purchase. That's because the natural ingredients in some soaps can get rancid or moldy.

However, it's likely that your soap is still effective, even after its expiration date. Here's what you need to know.

Soap does expire, but it's likely still effective

Soaps are surfactants, which reduce the surface tension of water and make the molecules slippery, causing soapy water to bond, trap, and loosen oil and grease — and the germs they contain.

That's why bacteria and viruses will physically slip off your hands when you wash with soap and water for 20 seconds, says Kevin Minbiole, PhD, an organic chemist at Villanova University.

According to Minbiole, soap also helps kill germs because of the polar and nonpolar ends in its molecular structure. The polar end helps soap dissolve in water, and the nonpolar end helps grab oil off your hands and carry it down the sink. It's the nonpolar end that disrupts the outsides of bacteria and viruses, causing them to burst and die.

Most manufactured soaps have an expiration date of two to three years. However, if soap still lathers up when you wash your hands, says Minbiole, it can still be used effectively — even after the expiration date. It shouldn't matter if the soap is liquid or bar, he says.

"If this expired soap… still lathers up and you know, gets all frothy and gets your hands kind of squeaky and cleaner at the end, you might be perfectly fine," says Minbiole.

How to know when soap is expired

A soap may be expired if it's cracked, dry, and doesn't lather up, or if it doesn't have the fragrant smell it did when you first bought it.

When compared to manufactured products, soaps scented with essential oils and colored with natural botanicals may have a shorter shelf-life as a result of the natural ingredients. These handmade, organic, or natural soaps should still function as well as store-bought ones, but they may expire earlier.

Essential oils are "volatile," meaning they tend to evaporate when exposed to air. Soaps can lose their scent when the essential oils providing those fresh smells evaporate, and some natural scented soaps even recommend use within three months after opening the box.

Another sign that soap is too old is orange spots. The orange color is due to the oil in the soap going rancid. Though still technically safe to use, the soap won't smell very nice.

Overall, as long as a soap hasn't gone rancid, grown mold, or no longer lathers properly, you should still be able to use it effectively after its expiration date.

• What temperature kills germs? How to use heat properly to get rid of bacteria and viruses
• Does alcohol kill germs? Yes, as long as the solution is strong enough
• Does vinegar kill germs? It isn't the best disinfectant for viruses
• The best hand soap
• The best hand sanitizer
• The best disinfecting cleaners
• Does hand sanitizer work? The difference between sanitizer and soap
• Hand sanitizer does expire — here's whether it's still worth using