Should You Wash Your Hair Before Colouring It?

Arriving for a colour treatment with freshly washed hair is not always the best option. Hairdresser Álex Sestelo advises keeping the hair clean while avoiding shampoo immediately before colouring, so that some of the scalp’s natural oils remain. This coating may lessen the discomfort caused by contact with chemical products.

Why is it not advisable to wash your hair immediately before colouring it?

The scalp continually produces sebum. This lipid layer coats the skin and can provide an extra barrier while colour is being applied. Washing, rubbing and rinsing the area shortly before using dye removes some of these oils, potentially making already sensitive skin more prone to stinging and irritation.

That does not mean oiliness prevents an allergic reaction. Ingredients found in certain hair dyes, particularly paraphenylenediamine, known as PPD, can cause contact dermatitis, including in people who have used similar products before. Natural oils provide limited physical protection, rather than a barrier against allergies.

Is it better to colour dirty hair?

Not necessarily. The aim is to avoid freshly washed hair, not to allow several days’ worth of sweat, heavy oiliness, dry shampoo, styling waxes or other cosmetics to build up. Residue on the strands can prevent the colour from making even contact with the hair fibre. Before colouring, the most suitable balance includes:

• hair that is clean but was not washed minutes before application;
• a scalp with no wounds, redness or irritation;
• strands free from an excess of waxes, oils and sprays;
• no itching or flaking caused by previous products;
• following the specific instructions for the dye being used.

Sestelo highlights the distinction between clean hair and freshly washed hair. According to the professional, it is a myth that dye will necessarily take better simply because the hair is very dirty. Keeping a small amount of oiliness is mainly intended to improve scalp comfort, rather than to make the pigment “take” more effectively.

What happens to the hair fibre during colouring?

With permanent hair colours, alkaline and oxidising agents allow colour precursors to work inside the hair fibre. This differs from simply depositing pigment on the surface, which is why the condition of the hair, the type of product and the processing time all directly affect the outcome.

This is also why there is no single preparation method for every hair dye. Permanent colours, semi-permanent colours, bleaches and plant-based products have different formulations and instructions. Guidance printed on the pack or provided by a professional should take precedence over general washing rules.

What care is important before applying hair dye?

More important than working out precisely how many hours have passed since the last shampoo is checking the condition of the skin. Colour should not be applied if the scalp is irritated, sunburnt, injured or clearly sensitive. Further precautions can reduce risks during the process:

• carry out the sensitivity test specified by the manufacturer before every application;
• wear gloves when handling the dye;
• follow the stated processing time exactly;
• avoid getting the product in the eyes;
• rinse the scalp thoroughly once the procedure is complete.

The test deserves attention even from people who have used the same shade for years. Sensitisation to particular ingredients can develop after previous exposure, and symptoms such as itching, stinging, redness, swelling or blistering are signs to stop using the product.

What is the best condition of the hair for colouring?

The ideal balance is to arrive with hair that has no excessive product build-up, while retaining the scalp’s natural oils by avoiding washing immediately before application. There is no need to deliberately leave hair greasy: the recommendation simply seeks to prevent shampoo, water and friction from stripping away this layer just before it comes into contact with chemicals.

Preparation must also take account of the type of colour and the condition of the skin. If there are wounds, stinging or irritation, postponing the procedure matters more than any rule about washing. When the scalp is intact, the hair is free from excess residue and the product instructions are followed, colouring is more likely to be carried out under favourable conditions for both skin comfort and even pigment distribution.