Best Shampoo for red hair

Washing with conditioner only is the best recommendation I can give. When I do this colour hardly fades at all, for weeks on end. It can be trial and error to get it right, but it's well worth it if you can.

Otherwise, I really never use a specific shampoo. What I find more effective is if my hair is all one colour I will add some of my dye, though only if it's a direct dye, so Adore, Directions, Manic Panic, etc (Adore has many several more natural reds) to my conditioner to have a top up each time I wash my hair. Even if it's a permanent dye you can use this method though. Just find the best match in Adore or which ever brand of direct dye you decide to go for. You can even mix dyes to tailor it exactly as they mix very well. www.beeunique.co.uk is a great source for these dyes

Other than that, yep cool water, wash as infrequently as you can. Try vinegar rinses too.