The main reasons for bad-smelling urine include dehydration, certain foods, vitamins or medications, and possible health conditions. When dehydrated, urine becomes concentrated with less water, causing a stronger ammonia-like smell. Foods like asparagus, coffee, and compounds in vitamins (especially B vitamins) can also cause a strong or unusual urine odor. Certain medications such as some antibiotics may contribute to this as well. Additionally, health issues like urinary tract infections, diabetes, liver or kidney disease, and some metabolic or genetic disorders can cause foul-smelling urine. If the bad smell persists or is accompanied by other symptoms, consulting a doctor is advised to rule out infections or other medical conditions.