Mixing bleach and vinegar is not recommended as it creates a harmful chemical reaction that releases chlorine gas. Chlorine gas is poisonous and can be fatal if inhaled at high enough concentrations. The acidic properties and chemical make-up of both bleach and vinegar can create a harmful chlorine gas and they should never be mixed together. Even small amounts of vinegar mixed with bleach can create this toxic gas. Symptoms of exposure to chlorine gas can vary based on the individual, but people who have underlying lung disease, such as asthma, may be more sensitive to the effects. If you accidentally mix bleach and vinegar, you should immediately leave the area and get into fresh air. If you experience symptoms such as difficulty breathing, coughing, or chest pain, seek medical attention immediately.