Chlorine is a powerful and dangerous oxidant and chemical gas. It is often used as a disinfectant that can be very irritating to the skin, eyes, and respiratory tract. It is found that children who swim regularly in indoor chlorinated pools have an increased risk of asthma and chlorine can cause problems with lung function, erosion of dental enamel, and increased risks of bladder cancer.

When high levels of chlorine come in contact with organic things, such as leaves and dirt, they can form other toxic substances called trihalomethanes, which can increase the risk of cancer, miscarriage, and birth defects. It is recommended to wear a mask or goggles when swimming in water with chlorine to protect the eyes. It is better to swim in outdoor pools than indoor ones because the gas in chlorine would be more dispersed. It is best not to swim in chlorinated pools everyday.