Maleic acid may inhibit certain enzymes in metabolism, such as aminotransferase in the metabolism of amine acid, which is mainly in liver and kidney. Therefore, long-term ingestion of maleic acid may cause liver and kidney damage.   In addition, some enzymes may also be affected by maleic acid in the Chemicalbook acid cycle of granulosomes, which may cause irreversible damage to renal tubules in dogs in animal experiments.   In animal experiments, the degree of injury is proportional to the dose and ingestion time.