Unexpected Causes of Fish Odor on a Baby

Does your formula-fed or breastfed baby's poop suddenly smell bad? Like fish? It could be anywhere from a very rare syndrome to very fishy burps.

Most parents enjoy the sweet smell of a newborn, but some babies may develop a fishy smell that’s not so pleasant. If that happens, it’s always best to check with your pediatrician about the cause and treatment. A fish odor may be the result of a genetic disorder, the baby’s diet or your choice of diapers and diaper cream.

Lookout: Fish Odor Syndrome

In rare cases, a fishy smell may be a sign of a genetic disorder called fish odor syndrome or primary trimethylaminuria. Dr. Andrew Weil, author and practitioner of integrative medicine, explains that babies with fish odor syndrome have an enzyme deficiency that prevents the body from breaking down trimethylamine 1. TMA is a byproduct of digestion released by bacteria in the stomach. Babies with fish odor syndrome release TMA through their breath, sweat and urine, and the smell can be mild or strong. The problem is not linked to hygiene, and there’s no cure, but a change in diet may help. The syndrome can be diagnosed through genetic testing. The NIH, U.S. National Library of Medicine, states that the disease is so rare that the incidence is unknown 5.

Cloth Diapers Retain Stench

Moms contributing to some online parenting forums complain of a fishy smell coming from their babies' diapers, not the babies themselves. Some have traced the smell to certain materials used in cloth diapers or an overuse of detergents used for cleaning the diapers. BornToLove.com suggests a number of ways to clean cloth diapers to reduce their smell 2. The site also suggests that some diaper creams may give diapers a fishy smell. Check the product label. Creams that contain cod liver oil may be to blame.

Fish Oil, Fishy Burps

Fish oil is a popular supplement among adults, and a frequent complaint among those who take the supplement is a fishy aftertaste or a fishy smell when burping. Although the Mayo Clinic says that fish oil supplements should never be given to children under the age of 18 unless a doctor recommends it, some parents add small amounts to baby formula to boost heart-healthy omega-3 fatty acids 3. There are studies that show that fish oil supplementation in early infancy can help decrease allergies 4. If you give fish oil to your baby, you might notice a fishy smell when burping your baby.