Most bamboo fabrics are semi-synthetic (bamboo rayon/viscose). The only bamboo fabric that would be fully natural would be bamboo linen, which is not a common fibre in yoga wear. Maybe this person isn't allergic to rayon, I just die on the hill that these bamboo fabrics are not actually true natural fibres, it's mostly a green washing thing. Rayon has some great properties, but I don't want people thinking bamboo rayon is any different than other rayons, they're just using different cellulose sources to mix with boatloads of chemicals.