Dental fluorosis is the appearance of faint white lines or streaks on the teeth that only occurs when younger children consume too much fluoride, from any source, over long periods when teeth are developing under the gums. Once teeth break through the gums, you cannot develop fluorosis. Fluorosis is a cosmetic condition that affects the teeth. It’s caused by overexposure to fluoride during the first eight years of life. This is the time when most permanent teeth. Fluorosis first attracted attention in the early 20th Century. Researchers were surprised by the high prevalence of what was called “Colorado Brown Stain” on the teeth of native-born residents of Colorado Springs. The stains were caused by high levels of fluoride in the local water supply. This was fluoride that occurred naturally in the ground water. People with these stains also had an unusually high resistance to dental cavities. This sparked a movement to introduce fluoride into public water supplies at a level that could prevent cavities but without causing fluorosis. Fluorosis affects nearly one in every four Americans ages 6 to 49. It’s most prevalent in those ages 12 to 15. The vast majority of cases are mild, and only about 2% are considered “moderate.” Less than 1% are “severe.” But researchers have also observed that since the mid-1980s, the prevalence of fluorosis in children ages 12 to 15 has increased. Although fluorosis is not a disease, its effects can be psychologically distressing and difficult to treat. Parental vigilance can play an important role in preventing fluorosis.