cotton on

リーダーズダイジェスト７月号のMORE THAN JUST PANDA FOODと題された記事からです。
Bamboo Skin Care: Beauty companies are cottoning on to bamboo's benefits, too. Finely ground bamboo is a natural exfoliant being added to face scrubs. And its high silica content makes its extract a good ingredient for shampoos and moisturisers.
"cottoning on" が分からないので調べます。
・OneLook Quick Definitions: understand, usually after some initial difficulty
・Dictionary.com:　cotton to or on to, Informal.
a. to become fond of; begin to like.
b. to approve of; agree with: to cotton to a suggestion.
c. to come to a full understanding of; grasp: More and more firms are cottoning on to the advantages of using computers.
・Wiktionary: (idiomatic) To realize; come to understand
同意語として "catch on" がある事が分かりましたが、すると過去形は：
"She didn't know what her classmates were plotting but finally caught on."
"caught on"、"cotton on" 発音が似ていますね。私の推測ですが "cotton on" は "caught on" から出来た用法ではないでしょうか？　（辞書に載っていた説ではありません。念のため。）
注：　"exfoliant": a cosmetic product or ingredient intended to remove dead skin cells and dirt from the skin surface (Dictionary.com)