I left the hair dye in a hot car… is it ruined? Can I still use it?

woman in the car clutches her head worried

  • If you leave the hair dye in a hot car, you shouldn’t use it. The ammonia and developer ruin when hair dye is exposed to the sun or high temperatures.
  • Therefore, if you apply that dye, you’ll only damage your hair.
  • If you notice the dye is dark after leaving it in a hot car, throw it away because it’s ruined. And if you see that the developer has a lot of foam, it’s also ruined and you shouldn’t use it.
  • The dye should always be stored at room temperature, away from humidity, high temperatures, and the sun


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 Did you leave your hair dye in a hot car and want to know if you can still use it? 


To begin with,  hair dye should NOT be exposed to the sun. 


Even without knowing the details, I’d tell you  NOT TO USE IT  because it’s probably spoiled.

Don’t feel guilty! It could happen to anyone.


In fact, I also live running against the clock. We get up early. We take the kids to school, see them off and wish them a good day.

We drive through half the city, and stop at stores to do the groceries. So, the car could be for a few hours under the hot sun.

woman keeping purchases in the car in the sun

When you get home, a phone call interrupts your task. Then, distracted, you leave some bags in the car under the sun.

A few hours go by, and when you are ready to dye your hair, you remember leaving the dye in the car in the sun. Oh my God! You run to the car like hell.

And when you get to the car, you can find two scenarios:

  • The bags are a mess because the contents of the dye spilled out. Yes, the heat made the plastic container open up like a small color bomb.
  •  You look at the dye and notice a strange color. 


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What should you do?  Throw it all out! Throw it away!  The dye exposed to the sun in the car has been ruined.

Why? That’s what I’ll tell you about.


Why is the dye ruined after sun or heat exposure?

hair dye that changed color comes out of the container

 Permanent dyes contain chemicals that degrade when exposed to heat or the sun. 


If you apply the degraded dye, it won’t change the color of your hair but it could damage it irreversibly.

Would you cook a chicken that has been exposed to the sun for hours? I think the answer is obvious: you wouldn’t. Without the slightest doubt, you would throw the chicken away to avoid poisoning your family.

If you leave the dye in the car in the sun, you should follow the same reasoning. In this case, you would ruin your hair.

It’s the same as if you apply the dye to your hair, and lie down on a deck chair in the sun to get a tan. You can’t go out in the sun with the dye on.


The dye contains ammonia, so the heat activates toxic vapors. Those vapors could change the color of the dye, swell the container, etc. This is the first sign that the dye has been ruined by exposure to the sun.

What’s more, the same could happen to the developer. In that case, you’ll notice foam on the surface.


 The dye is very sensitive to thermal changes. So, if you leave it in the car for 30 minutes,  you should discard it because it won’t work.

What happens if you leave the dye briefly in the car and under moderate heat?

woman puts hair dye in plastic container

If the dye didn’t burst and the developer isn’t foaming, the dye may still be working.


In this case, you’ll need to do the following:

  •  Let the dye sit at room temperature for a day  before blending the dye with the developer. Don’t place the dye in the refrigerator, because the cold temperature could dry out the developer and degrade it.
  • The next day, prepare the blend. Place the dye in the plastic container.  If it’s dark,  (not white nor yellow) it’s degraded after being in the car in the sun, and you should throw it away. The ammonia will also be degraded and useless.
  •  If the dye is white or yellow, but the developer is liquid,  you should also discard it because it has been ruined and is useless.



If you leave the dye in the car in the sun, you should throw it away because the chemicals in the dye have degraded. If you apply the degraded dye, you’ll ruin your hair.

Hair dye should always be stored away from heat and sunlight, at room temperature, and in a dry storage area.

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