Why Gray Hair Can Be Harder to Color, and What Research Shows

Research points to two differences between gray and pigmented hair that matter for coloring. Gray hair has no melanin for dye to build on, and gray strands often differ physically: in one study, white hairs were thicker than pigmented hairs and had a larger central core. Gray hair is also often said to "resist" dye, but a 2009 review in the International Journal of Trichology calls the evidence for that anecdotal. What the reviews agree on is that permanent dye covers the most gray, up to 100 percent, while milder dyes cover half or less.

This post is part of our guide to ways to cover gray hair.

What changes when hair turns gray

Hair gets its color from melanin. A 2014 review in Actas Dermo-Sifiliográficas explains that two types of melanin, eumelanin and pheomelanin, together with the total amount of melanin and the size of its granules, set each person's hair color. Hair with no melanin looks white because it scatters light. Our guide on how hair gets its color explains the biology, and the post on white hair versus gray hair looks at the difference between the two.

The loss of pigment is not the only change. A 2004 study in the European Journal of Dermatology measured 3,343 scalp hairs from women and compared white hairs with pigmented ones:

Measure	White hairs	Pigmented hairs
Average width	67.68 micrometers	57.41 micrometers
How developed the medulla was	23.91 percent	12.21 percent
Growth per day	0.38 mm	0.35 mm

A micrometer is one thousandth of a millimeter. The medulla is the soft core in the center of the strand, and the study scored it from 0 percent (absent) to 100 percent (fully developed).

The 2009 review adds more detail. It says the medulla in gray and white hairs is often enlarged and collapsed, forming a central cavity. It also reports that gray hair has been found to be more sensitive to weathering, to show chemical changes in its protein, and to react more strongly to oxidizing and reducing chemicals. Hydrogen peroxide, the developer in permanent dye, is an oxidizing chemical. For how these changes affect texture and daily care, see why gray hair feels different.

Is gray hair really resistant to dye?

The idea comes from reports and experience, and in the sources we reviewed it was not measured directly. The 2009 review says "anecdotal evidence indicates that gray hair is coarser and less manageable than pigmented hair," and that gray hair "is said to often fail to hold a temporary or permanent set, and to be more resistant to incorporating artificial color." The review treats these reports as signs of changes inside the hair fiber, not as measured results.

We did not find a controlled study that compared how much dye gray hair and pigmented hair take up. The measured differences above, in width, medulla, weathering and chemical reactivity, are real. How much each one affects a home color result is not clear from the sources.

Why dye type matters so much on gray

Gray hair has little or no pigment, so the dye has to supply all of the color. Different dye types do this with very different strength.

The 2014 review says permanent dye contains up to 6 percent peroxide and uses ammonia, which brings the mixture to a pH of 9 to 10.5 and helps it pass all the way into the cortex, the inner part of the strand. There, the dye forms color molecules too large to wash out. The review says permanent dye gives the highest gray coverage, up to 100 percent, "even with recalcitrant hair," meaning hair that resists color.

Milder dyes do less:

Dye type	Gray coverage	Why
Permanent	Up to 100 percent	A strong developer and ammonia carry the dye deep into the cortex
Demi-permanent	Up to 50 percent	A weaker developer (2 percent peroxide) and little alkali, so the dye does not reach as deep
Semi-permanent	Softens gray	Small, ready-made dye molecules stay in the outer layers and wash out over a few shampoos

A 2015 review in the International Journal of Trichology agrees that demi-permanent dyes are less effective on gray or white hair, and it says this is because they only reach the cuticle. Our page on permanent, demi-permanent and semi-permanent dye compares the three types in detail.

Why the same shade can look different on gray

When permanent dye goes on pigmented hair, the 2014 review explains, the first step is that the peroxide lightens some of the natural melanin. The new color then forms alongside the pigment that is left. On gray hair, there is little or no melanin to begin with, so the result comes mainly from the dye itself. That means the same dye can look different on gray strands than on the pigmented strands next to them.

What helps

• Match the dye to your goal. For full coverage, permanent dye is the type that can do it. For a softer look, demi-permanent or semi-permanent color, or gray blending and lowlights, may suit you better.
• Choose a shade near your own. The American Academy of Dermatology suggests staying within three shades of your natural color, and it says going darker is usually better than going lighter.
• Follow the timing exactly. The FDA says not to leave the product on longer than the directions say.
• Test every time. The FDA advises a patch test on your skin before every use.
• Ask a colorist if results are uneven. Tell them every product you have used, including any gradual or progressive color. The 2014 review notes that metallic dyes made with silver nitrate or lead salts are incompatible with hydrogen peroxide.

LIUMIQ is developing a gradual color product for gray hair. It is not for sale yet. Join the waitlist to follow the work.