There was a case where a person thought they were buying pure henna but it turned out to be a mix with other chemicals. This led to a really bad reaction on their scalp. Their scalp became red and inflamed, and there was a burning sensation. They had to wash their hair multiple times to try and get it all out, but it still took days for the irritation to subside. It's important to be careful about the source of henna to avoid such situations.
Sure. Some people have experienced that henna hair dye made their hair extremely dry and brittle. After using it, their hair started to break easily and lost its natural shine. It's likely due to the way the henna interacts with the hair's natural oils.