Milk thistle is a plant that's been used medicinally throughout the Mediterranean since ancient Greek times. Milk thistle seed extract contains silymarin, a mixture of flavonoids and polyphenols that have been researched for their potential antioxidant and liver-protective qualities. Milk thistle extract may support skin health by reducing the activity of collagenase (an enzyme that breaks down collagen) and elastase (an enzyme which breaks down elastin). It's also been researched for its potential to protect skin cells from depleting antioxidants like glutathione in response to UVA light exposure.