People new to hair dying are often confused by the difference between semi and demi-permanent hair color dyes. And that’s understandable – they sound so similar that you might even mistake them for synonyms. They are quite different, however, so let’s go into how they differ from one another here, as well as answer some other questions such as “Can you put semi-permanent dye over permanent?”, “Is semi or demi hair dye safer for your hair?”, and so on.
What is demi-permanent hair color?
Similarly to permanent hair color dyes, demi-permanent ones also contain peroxide in order to develop the hair and allow the pigment to penetrate the cuticle of the hairs. This is what makes them close-to-permanent, as their color doesn’t just coat the hairs but is incorporated into them. This is somewhat damaging for the hair, of course, which is why you need to take great care of it. Still, semi-permanent dyes are more sparing for our hair than permanent ones which is why they are often chosen.
And, if you’re wondering what does demi-permanent mean, the word “demi” comes from French and means “half”.
What is a semi-permanent hair color?
Semi-permanent hair dyes, on the other hand, don’t penetrate our hair’s cuticles at all and simply coat them with pigment. They are made to last as long as possible and good ones can maintain their color for up to 15 shampoo washes or even a bit more. Because they don’t penetrate the hairs, semi-permanent dyes are much safer to use but they need to be reapplied frequently if you want a permanent effect.
Consequently, because semi-permanent dyes don’t penetrate the hair, you can use them over hair that’s already dyed with permanent or demi-permanent dyes to enhance their effect.
Semi-permanent dyes work on the same principle as temporary ones but are different in that they do last longer. Temporary dyes, on the other hand, are washed away after just one or several showers at most.
Also, keep in mind that because they are just surface coating with no developer, semi hair colors are even more vulnerable to things such as direct sunlight, overly hot or cold weather, physical contact, and so on. Even a good semi-permanent hair dye can end up lasting only 3 to 6 washes instead of 15+ if you don’t protect your hair from the elements.
Demi-permanent vs semi-permanent hair dye uses
The long-lasting effect and the damage to the hair (or lack thereof) are the main differences between semi and demi hair color dyes. If you want a near-permanent effect and your hair is in a good enough condition to survive a bit of peroxide, you can go with a demi-permanent dye or even consider a permanent one. If, however, you want to spare your hair the damage of peroxide, using a semi-permanent dye once every several weeks can be a good alternative.