Hydrogen peroxide is a chemical compound widely recognized as a mild household antiseptic and disinfectant. The solution typically sold in drugstores is a 3% concentration, which is powerful due to its oxidizing properties. Because it kills bacteria, some people use it as an oral rinse for minor gum irritation or for a whitening effect. However, the 3% solution is intended for external use, and using it undiluted in the mouth can cause significant problems.
Immediate Reactions in the Mouth
When undiluted 3% hydrogen peroxide contacts the delicate tissues inside the mouth, the most noticeable immediate reaction is intense, rapid foaming. This effervescence is a chemical reaction where the enzyme catalase, naturally present in human tissues, rapidly breaks down the \(\text{H}_2\text{O}_2\) into water and oxygen gas. The rapid release of oxygen gas causes the solution to bubble vigorously, indicating a strong chemical interaction with the oral lining.
This chemical interaction quickly leads to a sharp, burning, or stinging sensation in the gums, tongue, and inner cheeks. Within moments, the mucosal tissue, particularly the gums, may turn white or blanch temporarily. This transient whitening occurs because the oxidizing agent causes temporary tissue ischemia, or a reduction in blood flow, and denatures the proteins in the top layer of the soft tissue. The experience is often accompanied by an unpleasant, metallic taste that lingers after the rinse.
Risk of Serious Tissue Damage
Using the undiluted 3% solution for more than a brief contact period risks serious structural damage. The high concentration acts as a caustic agent, causing painful chemical burns to the sensitive gingiva and mucosal lining of the mouth. Prolonged exposure to this undiluted strength can cause extensive injuries like ulcers and erosive changes in the oral mucosa.
In severe cases, sustained oxidative stress can lead to tissue necrosis, the irreversible death of cells in the affected area, particularly in the gums and cheek lining. Repeated use of undiluted hydrogen peroxide can also contribute to gingival recession, where the gum tissue pulls back from the teeth, exposing the roots. Beyond the soft tissues, the strong oxidizing action can affect dental structures, increasing tooth sensitivity. While low-concentration peroxide is used for whitening, chronic misuse of high concentrations can result in enamel erosion over time, making teeth vulnerable to decay.
Hazards of Accidental Ingestion
If undiluted hydrogen peroxide is accidentally swallowed, the hazards extend beyond the oral cavity to the entire upper gastrointestinal tract. The oxidizing agent can cause irritation and chemical burns to the lining of the esophagus and stomach, similar to the damage seen in the mouth. The most immediate systemic risk comes from rapid gas formation, as the swallowed peroxide is broken down by the body’s internal catalase.
This rapid decomposition releases a large volume of oxygen gas into the stomach, causing gastric distension, severe bloating, and belching. A rare but dangerous complication is the formation of a gas embolism, where oxygen bubbles enter the bloodstream through the stomach or intestinal walls. These bubbles can travel through the circulatory system and block blood vessels, which is a life-threatening condition that may cause symptoms like chest pain, confusion, or difficulty breathing. While small amounts of the 3% concentration are generally considered low-toxicity, consuming a large quantity can lead to severe internal injury.
Proper Dilution and Usage for Oral Rinsing
To use hydrogen peroxide safely as an oral rinse, it must be properly diluted to a much lower, less caustic concentration. The standard household 3% solution should be mixed with water to reduce the concentration to approximately 1.5% or less. A common dilution method is mixing one part 3% hydrogen peroxide with one part water for a 1.5% solution, or one part peroxide with two parts water to achieve a 1% solution.
This diluted mixture should only be swished in the mouth for a short duration, typically no longer than 30 to 60 seconds, and then spit out completely. It is important to never swallow the rinse, even when diluted, and to rinse the mouth thoroughly with plain water afterward to remove any residue. Hydrogen peroxide mouthwash is not intended for daily, long-term use and should be reserved for short-term situations, such as managing minor gum inflammation or post-procedure care. Individuals considering regular use should always consult with a dentist or physician first.