Hydrogen sulfide (H₂S) is a colourless gas that smells like rotten eggs. At high levels, it is flammable (can catch fire) and can be harmful to your health. 

This gas can form naturally in places like old water wells, oil and gas wells, sulfur springs, and swamps. It can also be made when dead plants or animals rot. This happens in places like animal farms, factories, sewers, or places that clean dirty water. 

Hydrogen sulfide is found in nature. You can be exposed to it if you breathe it in, eat or drink something that has it, or if it touches your skin. Your body does not store hydrogen sulfide. Once it enters your body, your liver breaks it down and you get rid of it through urine. 

Hydrogen sulfide usually breaks down in the air. So, it is only a health concern if you are close to a steady source of the gas, especially in a small, closed-in space. 

Exposure to low levels of hydrogen sulfide (10–100 ppm) may cause: 

• Irritation in the eyes, nose, or throat 
• Trouble breathing, especially for people with asthma 
• Headaches 
• Feeling tired 
• Trouble remembering things 
• Balance problems 

Short exposure to high levels of hydrogen sulfide (over 500 parts per million) can cause loss of consciousness (fainting). Most people wake up feeling fine, but some may have long-term issues. These can include headaches, memory problems, or difficulty moving. Very high exposure to hydrogen sulfide can be deadly. 

If your well water has hydrogen sulfide, it might smell like rotten eggs and taste like sulfur. The smell can get stronger when the water is hot, like during a shower, because the heat pushes the gas into the air. 

Water samples submitted to CK Public Health Clinic Services are only tested for bacteria. If you want to test for hydrogen sulfide or other chemicals, you’ll need to pay a private lab. If hydrogen sulfide keeps showing up in your water, there are special water treatment devices that can remove it. A licensed plumber or water treatment company can help you choose the best one for your home.