While mouthwashes are generally safe, some can cause side effects in patients who use them. Many over-the-counter mouthwashes contain high levels of alcohol that may range from 18 percent to 26 percent. This is a higher concentration of alcohol than is contained in some alcoholic beverages, such as beer or wine. Habitual use of these rinses can create a burning sensation in the cheeks, teeth and gums.

The alcohol in mouthwash may also contribute to dry mouth, which can increase a patient’s risk of tooth decay. Concerns have been raised about the risk of oral cancer due to alcohol contained in mouthwashes. However, there is currently no clear evidence that supports this.

Overuse of certain types of mouthwash (e.g., antiseptic mouthwashes) can upset the natural balance of bacteria in the mouth, and lead to bacterial overgrowth and conditions such as black hairy tongue.

Over-the-counter and prescription mouthwash can have a variety of side effects. Generally, these are more likely to occur with prescription strength rinses, but may also occur with over-the-counter mouthwash. Side effects include:

• Staining of teeth and/or dental restorations
• Taste disorder (dysgeusia)
• Build-up of tartar on the teeth
• Mouth and tongue irritation or numbness
• Mucosal erosions
• Retention of sodium
• Swollen glands on the side of the face or neck
• Sensitivity of tooth roots
• Mouth ulcers

Patients should inform their dentist about any side effects they continue to experience as the result of using a mouthwash. A dentist may be able to recommend alternative treatments, based on a patient’s dental needs.

There have been some concerns that the oils in mouthwashes may damage dental restorations, such as braces, dentures or tooth fillings. However, studies have shown that these oral rinses are gentle on restorations and do not cause damage.

Swallowing too much mouthwash can have serious side effects that require emergency medical treatment. Most commercial mouthwash contains alcohol, which may be lethal when consumed in large quantities by children. Many rinses also contain sodium fluoride, which can lead to fluoride toxicity when taken excessively or swallowed. Symptoms of mouthwash overdose include:

• Breathing problems, such as deep breathing (which may be rapid), rapid shallow breathing, slowed breathing or cessation of breathing.
  
  
• Gastrointestinal problems, such as abdominal pain, diarrhea, and nausea and vomiting.
  
  
• Nervous system problems, such as coma, dizziness or drowsiness.
  
  
• Bluish skin (lips and fingernails).
  
  
• Collapse.
  
  
• Convulsions.
  
  
• Decreased blood pressure (hypotension).
  
  
• Decreased urination.
  
  
• Excessive sweating.
  
  
• Excessive thirst.
  
  
• Listing from side to side or inability to walk normally.
  
  
• Slurred speech.