How often can I use it to keep the chestnut tone fresh?

Tinting shampoos are designed to be used intermittently, not as a daily cleanser. The pigments rinse out gradually with each wash, so most people reapply once the chestnut warmth starts to dull — often every 3–5 shampoos, depending on how frequently you wash, your water hardness, and how porous your hair is. Using it every time you shower can lead to pigment buildup (making the tone look flat or muddy) and may dry the hair because the surfactant base is formulated for deposit, not daily gentle cleansing. A practical routine: alternate with a sulfate-free, color-safe shampoo for regular washes, and bring in the tinting shampoo when you notice the tone fading. If your hair feels dry or the scalp gets irritated, extend the interval and add a hydrating mask. Always follow the leaflet's recommended leave-on time; leaving it longer won't make the color "stick" better — it only deposits more pigment in that session, which still washes out at the same rate.