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Not sure if that expired bottle of shampoo is still usable? Don’t worry. You’re not alone. Half-empty bottles of shampoo are pretty common in many bathrooms.

But if those bottles have been sitting around for too long, you might be wondering whether they can still do their job — and whether there are any risks involved with using expired shampoo.

Before you lather up, check out what there is to know about shampoo expiration dates, how to tell if a bottle of shampoo is past its prime, and what may affect the shelf life.

The short answer is maybe. Manufactures of personal care products such as makeup and skin care or hair care products aren’t required by law to label a product with an expiration date.

That said, many will include a “period after opening” suggestion, which generally refers to the length of time you can expect a product to work as it should or be safe for use, according to the Food and Drug Administration (FDA).

To locate a period after opening label on your shampoo, look at the back of the bottle, toward the bottom. If your product has a recommended “use by” date, you’ll see a symbol that looks like a small container with the lid off.

On the container, there will also be a number with the letter “M,” which stands for “months.” Most likely, it will be:

  • 12 M
  • 18 M
  • 24 M

This means the manufacturer is saying that once you open a shampoo bottle, you should use it within a certain time frame — usually 12 months, 18 months, or 24 months.

Sometimes, a product doesn’t come with information about expiration dates, period after opening time lines, or shelf life suggestions, making it a bit trickier to determine when you should toss a bottle of shampoo.

That said, you can still inspect the product to see if it has gone bad.

If your shampoo doesn’t have an expiration date or you’re not sure if it’s usable, there are a few signs to look out for, according to Gina Rivera, founder of Phenix Salon Suites.

Some telltale signs include shampoo that:

  • has an odd odor
  • has become clumpy
  • looks discolored
  • doesn’t seem to be working as it once did

To ensure your shampoo doesn’t lose its effectiveness before its recommended use by date, be sure to:

  • Close the lid all the way once you’re done using it.
  • Keep unopened shampoo away from high heat or direct sunlight.
  • Store the shampoo bottle in a cool, dark place.
  • Minimize exposure to water droplets or other products that may contaminate the product.

When shopping for a shampoo, Rivera noted, it’s important to recognize that organic products and products that are sulfate-free may have a shorter shelf life.

“This is due to the lack of preservatives and the addition of more health-based ingredients,” she explained.

“Expired products undergo a chemical change, which means they’re no longer effective at a high level,” Rivera said.

Using shampoo that’s past it’s use by date can result in your hair looking dull and not as clean as you’d expect.

At the more extreme end, Rivera explained, an expired product may cause itching or irritation to your scalp due to the shampoo’s chemical change.

Your bathroom is full of products that can go bad within a matter of months. That’s why it’s important to periodically take inventory of your health and beauty products and throw away any that are past their expiration date.

In addition to shampoo, here are some other items to check:

  • Makeup. The clock starts ticking once you crack open an eye shadow container or tube of lipstick. Like shampoo, your makeup may come with a period after opening label on the back of the bottle. Check this first and then use it accordingly. If it doesn’t have a label, most cosmetics are good for 3 to 24 months. Mascara is usually the first to go, at around 3 months, and lipstick the last, at around 18 to 24 months, according to the FDA.
  • Toothpaste. Toothpaste is required to have an expiration date. To locate the date, check the box and the tube of toothpaste. Always look for the American Dental Association Seal of Acceptance for maximum safety and efficacy.
  • Sunscreen. Your sunscreen should come with an expiration date. If your sunscreen doesn’t have an expiration date, the FDA says to discard it 3 years after purchase. If you use it beyond this date, the ingredients may not have the ability to protect you from the sun.
  • Hydrogen peroxide. It’s best to use hydrogen peroxide within 2 to 3 years after purchase. However, once you open the container, it’s only effective for 1 to 6 months.
  • Rubbing alcohol. To ensure effectiveness, use rubbing alcohol before the printed expiration date. This is generally 2 to 3 years after purchase.

Shampoo products aren’t required to have an expiration date, but many of them do come with shelf life or “period after opening” date.

If you can’t locate a label on your shampoo, be aware of any:

  • odd odor
  • discoloration
  • changes in the texture or color of the product

These can all be signs that it’s time to buy a new bottle of shampoo.