A brand linked to a mainland beauty blogger’s social media account has been exposed for making false claims about the “anti-ageing” ingredients in one of its products, prompting the blogger to offer a huge refund.

A kilogram of jasmine oil can cost $5,000. But to get that small amount of oil, harvesters need to handpick over 5,000 jasmine buds. Once the flower blooms, producers in India quickly process it into one of the priciest absolute oils in the world. Today,...