After 10 years of adult acne (in my 40s-50s) caused apparently by hormonal issues and controlled with low-dose tetracycline, I began using red/blue light therapy, specifically the "Acne Light" by Verilux. Over the past two years I have had almost no acne problems unless I go for several days without using the light (15 minutes per day several times a week). The company's literature says that light therapy works for about 75% of people with mild to moderate acne.