Ammonia, soda, sodium, and potassium hydroxide are key dirt-dissolving alkalis, which are able to remove stubborn grease and oil-based residues (e.g. in ovens) and obstructions (e.g. in drains). Alkalis are, however, unable to dissolve lime. Cleaning agents which primarily consist of strong bases are highly corrosive. Hazard labels and safety notices must be closely observed at all times.