Collagen is the glue that holds our skin, bones, cartilage, and blood vessels together, but the levels we produce it at decrease with age. "It's a little bit like a bubble wrap analogy, that with repetitive use some of the bubbles get popped," explains Dr Louise Reiche, president of the NZ Dermatological Society. Enter supplements: made from connective tissue in cows, pigs, or fish, what was once targeted at people with joint issues is now a beauty behemoth. Many influencers fill their social media feeds with collagen products, swearing their skin, nails and hair have never been better. But Dr Reiche insists it's a placebo.