Paralytic shellfish toxins (PSTs) are harmful substances produced by certain types of marine algae, particularly those in the genus Alexandrium. These toxins can accumulate in shellfish, such as clams and mussels, when they feed on the algae, making the shellfish dangerous for human consumption. When ingested, PSTs can cause serious health issues, including paralysis and respiratory failure. Symptoms may appear within hours and can include tingling, numbness, and difficulty breathing. Monitoring and regulation of shellfish harvesting are essential to prevent poisoning from these toxins, especially in areas prone to harmful algal blooms.