As the most abundant protein in the human body, collagen is undeniably important—and consuming supplements could help up your body’s levels. But if you’re new to the collagen train, you might be wondering when you should hop on. In terms of collagen degradation, sun exposure is one of the worst offenders. (It’s also one of the easiest to change, by the way.) “UV light exposure causes generation of free radicals, [which] trigger reactions that damage healthy cells,” explains Blair Murphy, M.D., FAAD, board-certified dermatologist. In the skin, “this oxidative damage breaks down collagen.” Other harmful habits include eating excess sugar, smoking cigarettes, and environmental pollution. Even lack of sleep and poor nutrition can speed up collagen decline. If (or when) you decide to add supplements to your routine, it’s crucial to know what they can’t do: Collagen supplements won’t reverse deep, pronounced lines—nor can they lift very loose skin. Basically, they won’t magically vanish existing, severe signs of aging. “You can use collagen to reverse minor things, like crow’s feet around the eyes but not once the skin’s gotten too leathery and damaged,” explains functional medicine doctor Robert Rountree, M.D., in mbg’s podcast. Therefore, it’s best to use them as a preventive method to avoid signs of aging—and to make sure they don’t worsen over time. While you’re at it, Murphy recommends defending your skin from sun exposure as early as possible. This will safeguard the collagen you already have and set you up for a lifetime of excellent sun protection habits. “It’s easier to prevent collagen loss in the first place than to stimulate new collagen formation and replace it later in life,” she adds.