Dehydration: This is a common cause of concentrated urine, which can have a strong, foul odor. The lack of sufficient fluid intake leads to a decrease in urine volume, resulting in a more concentrated urine that smells worse than usual.

Dietary factors: Consuming certain foods like asparagus, garlic, or onions can give urine a strong odor due to the breakdown of sulfur compounds.
Medications: Some medications, such as vitamin B6 supplements, can alter the smell of urine.
Bowel obstruction or constipation: In some cases, a bowel obstruction or severe constipation can cause urine to have a foul odor due to the reabsorption of toxins from the bowel into the bloodstream and then into the urine.

Diabetes: Although less common, uncontrolled diabetes can lead to a fruity odor in the urine due to the presence of ketones. However, in some cases, especially if there's an infection, the urine might have a foul smell.
Kidney stones: While not typically associated with a foul odor, some kidney stones, especially those causing obstruction, can lead to urinary tract infections or concentrated urine, both of which might result in foul-smelling urine.

Maple syrup urine disease: A rare genetic disorder that causes urine to smell sweet, like maple syrup, but in some cases, might be perceived as foul due to the accumulation of branched-chain amino acids and their metabolites.
Phenylketonuria (PKU): Another rare genetic disorder that can cause urine to have a musty or foul odor due to the accumulation of phenylalanine.
Urinary tract malformations or fistulas: Rare congenital anomalies or acquired conditions that can lead to the mixing of urine with fecal matter, resulting in a foul odor.