Check the expiration date stamped on the bottle.

If there is no expiration date on the bottle, then it probably isn’t safe to use. If you’re unsure about when your dye was manufactured or if it’s expired, look at the ingredients list.

If a chemical ingredient has an asterisk (*) next to its name, it means that it doesn’t have a known shelf life. For example:

• P-Phenylenediamine (D&C Violet No. 2) can be used safely for up to two years after opening if kept in a cool place away from direct sunlight and heat sources like radiators or heating vents (source). That means if you see P-Phenylenediamine listed as an ingredient without any asterisks next to its name, then it’s safe to use even if your bottle has been sitting around for ages!

Smell it.

Smell your hair dye.

This is the most common way to tell if hair dye has expired, and for good reason: if it smells off, it’s probably expired. Hair dyes contain harsh chemicals that are very potent in small doses and can quickly burn off your nose hairs if you’re not careful. If you’re using a liquid dye, check to see if the color is still fluid—if it’s separated or oxidized (the pigments have dried), then the product has likely gone bad.

If you’re unsure about whether or not your hair product should smell like this, consider how long ago you opened it up: some dyes last for months and others will only last a few weeks once opened before becoming unusable due to oxidation or separation of ingredients.

Shake it.

Shaking the bottle is one of the best ways to tell if your dye is expired. It helps mix the color dye with the developer, which you need for the dye to work properly. If you don’t shake it well before applying it to your hair, you may end up with patches of missing color or no color at all in certain areas.

Shaking also ensures that all of the ingredients have been thoroughly blended together and are ready for use without risk of damaging your hair or scalp by being applied before it’s completely mixed together.

Do a color test and a strand test.

A good way to tell if your hair dye is expired is the color test. Put a small amount of the dye on a white cloth or paper towel and look at it. If it’s still vibrant and looks just like it did when you bought it, then chances are everything is fine. However, if the color has faded or dulled over time, then that means your product has expired and you should probably toss it out.

Another way to test whether or not your hair dye has gone bad is by doing a strand test on some strands of clean hair (don’t use any strands from an existing dye job). If there isn’t any reaction after leaving them in for 24 hours, then this means that whatever reactions might have occurred—whether chemical or biological—are no longer happening because all traces of chemicals have been removed from those strands (at least until there’s another chemical reaction!).

Does your hair dye have ammonia or peroxide?

The first thing you can do to test if your hair dye is expired is look at the ingredient list. If there’s either ammonia or peroxide in the list, it’s likely past its expiration date. You may be thinking, “but what about those professional dyes like Pravana and Schwarzkopf that have peroxide?” The reason why these types of products work so well is because they contain a higher concentration of ingredients than drugstore varieties… so even though they have peroxide in them, it’s not as bad for you (or rather, it won’t have anywhere near as much negative impact on your health) when compared to regular box dyes made at home!

The next step would be to check the package itself: some companies put an expiration date right on their packaging; if yours doesn’t say anything about an expiration date then try looking up information online about how long these kinds of products are good for before using them again (the FDA doesn’t require manufacturers to provide this info).

You can tell if your hair dye is expired by checking for an expiration date, smelling it, shaking it, and doing a color test and a strand test with ammonia or peroxide.

You can tell if your hair dye is expired by checking for an expiration date, smelling it, shaking it, and doing a color test and a strand test with ammonia or peroxide.

If there is an expiration date printed on the box of hair dye you’re using, check that first. If there’s no expiration date printed anywhere on the box (or even an “expires” one), then look at it carefully to see if there are any signs of deterioration. Is it crumbly? Does it have any weird smells? Does the texture feel gritty when you rub some between your fingers?

If all signs point to no signs of deterioration or signs of improvement (slightly improved appearance), go ahead and use your dyes!