Could CO/no-sulphate shampoo wash out henna?

[Mononoke]

A few washes ago I finally switched from regular shampoo to a no-sulphate one. I also did one or two CO-washes.
Today a friend brought my attention to the fact that my hennaed hair is not as red as it used to be, and I've noticed too that the color seems closer to my natural color.

Could any of the above have some effect on the henna?
Also, does chelating shampoo wash out henna?

Thanks in advance for any help!

[oktobergoud]

No, I don't think so. I co-wash and use sulphate-free shampoo and I don't think it washes out my henna at all!

Maybe it's just oxidizing? Have you just used henna? To me, henna really looks different in every light, so maybe it was just coincidence?

[Mononoke]

No, I hennaed about a month ago and it was about the same color between oxidation and a few days ago.