Dye molecules are large, which means they can’t easily penetrate the hair shaft.

Hair dyes contain large molecules. This means they can’t easily penetrate the shaft of your hair. When you apply a chemical dye to your hair, it’s actually sitting on top of your scalp and not going inside it at all. The roots of your hair will absorb some of this dye, but most of it stays on top and flakes off as you wash.

Dye molecules are about two times bigger than the cuticle layer surrounding each strand, which means that even if you squeeze hard enough for a long time (and believe me, I’ve tried), no amount of rubbing can make one go down inside the hair shaft!

What about permanent dyes?

Permanent dyes are made of chemicals that damage the hair shaft with bleach or ammonia (or both), so they’re best left to professionals. If you’ve tried semi-permanent dyes, then you know they work by penetrating the hair shaft more easily than permanent dyes do. That’s because their molecules are smaller and therefore can slip through even tightly packed cuticles in the cortex of your hair.

In fact, that’s why it’s better to use semi-permanent dye over processed color: these types of dyes are gentler on your hair because they don’t cause as much damage when deposited into your strands during application.

You can also use tools to help your hair dye stay on longer.

You can also use tools to help your hair dye stay on longer.

• Use a hair oil. Hair oils are great at keeping your scalp moisturized, which adds shine and keeps the dye from washing out as quickly. We recommend our favorite, the Shu Uemura Art of Hair Essence Absolue Oil.
• Use a heat-protective spray before you curl or straighten your hair. The heat from styling tools can open up the cuticle and let some dye seep out, so protect yourself by applying a heat-protecting spray like Bedhead Superstar Queen for a Day Super Shiny Dry Shampoo to dampened strands before styling them with hot tools like curling or flat irons or blow dryers (or even just run them under warm water).
• Use dry shampoo in between touch-ups if you’ve already got grey roots (which is why we love this one from Klorane—it covers grey better than most other dry shampoos). If you’re trying to keep processed colour in place for as long as possible without having more salon visits every couple weeks, using dry shampoo whenever it’s time between touch-ups will help keep those roots looking fresh while keeping any grey hairs hidden under all that lovely dye!

What are the best products and techniques?

• Use a heat protecting spray before using your hot tools.
• Use a hair oil to lock in the color.
• Wash your hair less frequently.
• Use a hair mask every so often to keep your strands nourished and hydrated.
• Instead of using sulfate-free shampoo, use a color-protecting shampoo and conditioner that helps prevent fading caused by water or shampooing too often.

The best way to keep your color locked in is by using a hair oil and a heat-protective spray.

The best way to keep your color locked in is by using a hair oil and a heat-protective spray. You can apply the oil on wet or dry hair, and it’s best to use it on the ends of your hair (not at the roots). If you’re going to use a blow dryer or curling iron, make sure you apply the oil before using any heat tools. It will help protect your color from fading or being damaged from those tools.

The heat-protective spray will also help lock in your color for longer lasting results! It protects against damage caused by thermal styling tools such as flat irons and curling wands, which can make your dyed locks fade faster than usual. Simply spritz some onto damp strands right before styling them with any type of device mentioned above — but only after applying an ample amount of moisturizing products beforehand!