Harmful effects of fluoride include swelling of the lips, mouth, tongue and face, chest congestion, and trouble breathing, states Drugs.com. Taking high amounts of fluoride can result in problems with the nervous system and muscle weakness, according to WebMD. Low doses of fluoride cause no common side effects.
When taken in large doses, fluoride can result in hives, itching and rash, explains Drugs.com. Fluoride can cause weak ligaments and bones, according to WebMD. Additionally, the chemical can discolor teeth in children whose teeth are still growing. Children should avoid swallowing toothpaste and fluoride rinses. Pregnant women and breast-feeding mothers should take care not to use large amounts of fluoride-containing substances.