Does Wash In Wash Out Colour Do Much/any Damage The Hair?

If it says it only will last a few days or week, it won't damage the hair  because it only sits on top of the hair and  it can only enhance your hair or make it darker and shineier, s o it can be good for the hair. Some colors say it will last a month or so and it will contain a low % of peroxide. If you chose a color that is lighter than your own hair it can actually lighten your hair and that can cause a little bit of damage depending on the health of your hair before you colored it. Some times hair is to healthy and it lays flat and you can't get it to hold a style, in that case you want a little damage if you want your hair to do more than lay flat.With the color that has a little peroxide it will last longer but pick a color that is not lighter than your own that way you wont have darker roots when the color grows out and the color won't be permanent.

All hair dyes, hair wash like shampoos and conditioners contain chemicals and preservatives which can damage hairs but not necessarily in every individual. Some peoples are sensitive to these ingredients and face hair damage.

Any repeated use of hair dye is damaging. Especially bleaching.Wash dyes are less damaging to your hair. I would use the wash dyes for now until the bleached portion gets long enough to cut. Then see a real hair specialist about less damaging options for the future.

on bleached hair >don't do it!!!!!