That sunscreen you've had sitting in your cabinet for multiple summers does in fact have an expiration date.

But how long is too long to go without swapping it out?

According to Megha Trivedi, assistant professor of dermatology at RUSH Medical College, sunscreen should be replaced at least every three years.

"Now, that being said, if you are using your sunscreen correctly, you should be going through a bottle much sooner than three years," she told NBC Chicago. "But typically, if something is sitting there and you're not sure that's kind of the timeframe you want to use."

The U.S. Food and Drug Administration requires sunscreen to maintain their original strength for that time frame.

Here's what you should know about sunscreen this summer:

Signs your sunscreen is expired

What if you don't know how old your sunscreen is or you suspect it may be going bad sooner than expected?

Trivedi said it depends on the type of sunscreen.

"Mineral sunscreens are typically more photo stable ... usually you want to store sunscreen in a cool, dark place, and that helps it to become a little bit more stable, lasting a bit longer," she said.

Trivedi said she uses three major indicators:

1. Color

"So, you know, if you had a sunscreen that has certain color when you bought it, but now it's a little bit more brown or it's just off," Trivedi said.

2. Consistency

"So if you have a sunscreen that was perhaps a little thicker when you first bought it and now it's more watery or it's grittier, you know, it's clumping together, that's another sign that it might not be as good," Trivedi added.

3. Odor

"So, I know sunscreen sometimes does not smell good, but typically you can tell when you first bought the sunscreen versus, you know, a few years later, that sunscreen does have, quote unquote, a funky odor," she said. "And that's the one that you want to, you know, say, 'OK, maybe I'll invest the new sunscreen at this time."

What happens if you use expired sunscreen?

Trivedi said using expired sunscreen can lead to decreased protection and increased risks of UV damage, including the potential to lead to skin cancer.

Ways to preserve your sunscreen

According to the Mayo Clinic, there are steps you can take to preserve your sunscreen too.

1. Avoid exposing the container to excessive heat or direct sun
2. Place sunscreen containers in the shade or wrap them in a towel
3. Discard sunscreen that has any obvious changes in color or consistency

What is the best sunscreen?

"The best sunscreen is the one that you are going to use," Trivedi said.

But here's what she looks for as a dermatologist:

• SPF 30: "That's going to be very important."
• Mineral vs. chemical: "A lot of people don't prefer a mineral sunscreen just because it does go on a little bit more white; however, I actually say if you can tolerate it now - there's many different formulations out there that go on a little bit more sheer- I would pick a mineral sunscreen and the reason is mineral sunscreens are more broad spectrum, so they make sure it covers you from UVA, UVB and for two other reasons."