Why Does My Baby’s Urine Smell So Bad? (Here’re 7 Reasons Why).

Why Does My Baby’s Urine Smell So Bad - Babe in Dreamland

Healthy urine is usually clear or pale straw in colour and has a mild smell. It means that baby is well-nourished and hydrated.

But what if my baby’s pee has a strong or foul-smelling odour?

Most of the time, smelly wee is nothing to worry about. But some instances require medical attention.

Let’s discuss the 7 possible reasons for smelly urine in babies.

Why Does my Baby’s Urine Smell So Bad?

Foul-smelling urine in babies doesn’t always indicate a health issue, but it certainly shouldn’t be ignored. One of the most common reasons is a urinary tract infection that needs antibiotic treatment. Smelly pee may also mean that your baby is dehydrated, which should be addressed urgently. The less severe reason includes the side effect of a specific food, medication, or vitamin B supplement. There are also rare genetic disorders that may explain the foul-urine smell. These include maple syrup urinary disease or fish odour syndrome (trimethylaminuria).


1. Urinary Tract Infection (UTI)

A urinary tract infection is a common condition affecting babies – primarily girls.

UTI is caused by bacteria entering the bladder or kidneys through the urethra.

And this can easily happen if the baby wears a soiled nappy for a prolonged time or when the baby’s bottom isn’t thoroughly cleaned after a poo.

In such cases, the poo (and the germs) particles can enter their urethra, causing an infection of the urinary tract.

Also, babies who suffer from constipation are more vulnerable to UTIs.

Although UTI is generally a mild illness, it requires a course of antibiotics to clear out.

If untreated, it may lead to more severe complications affecting the kidneys.

Because of the generic nature of the symptoms, it may not be easy to spot UTIs in babies. And these symptoms are common for several different conditions. But, you should look out for the following signs:

  • Foul-smelling urine that may be dark, cloudy, or containing blood
  • Urine frequently
  • High temperature
  • The baby appears unwell and unsettled or irritable.
  • Baby refuses to eat
  • Vomiting

So, if you suspect a UTI in your baby, you should consult the doctor without hesitation.

UTIs won’t go away without antibiotic treatment!

Did you know babies and children can get urinary tract infections?

2. Dehydration

Smelly pee may also mean that your baby doesn’t take enough fluids.

Which, I know, may seem strange given that babies are solely on a liquid diet during their first few months. And they seem to be feeding practically all of the time.

So how come a baby may be dehydrated?

First of all, the baby’s stomach is tiny and has no capacity to reserve much fluid.

Furthermore, babies may not be as effective feeders as we expect them to be.

They may have difficulties latching on to the breast, swallowing, or even digesting the milk. Also, they may vomit excessively as a result of acid reflux. 

(I talked about more in my post How Can I Help My Baby With Acid Reflux?)

So, except for the smelly wee, which is also highly concentrated and of dark colour, another sign of dehydration is very few wet nappies. Dehydrated babies generally appear unwell, cranky, and tired.

Also, their eyes and soft spot may look sunken, the skin may look wrinkly, and sometimes they may have diarrhoea.

Dehydration can be dangerous in young babies, and they will need to get the fluid replaced immediately. So, you should keep feeding your baby milk as often as possible.

And remember, if your baby shows symptoms of dehydration, you should call the doctor for further advice.

3. Food

Did you know that certain foods can give urine a strange, strong odour?

The reason for this is that these foods contain some components that have a naturally occurring strong odour.

These foods include asparagus, garlic, onion, salmon, curry (specifically cumin and coriander in curry), brussels sprouts, broccoli, cauliflower and fenugreek.

Naturally, this reason applies to babies who are already on solids. So, forget it if your baby is still only on milk.

Furthermore, some foods that contain sulphur can make the wee smell of rotten eggs.

I talked about other side effects of a sulphur-rich diet in the post: Why Does My Baby’s Gas Smell Bad?

 4. Medication

If your little one is taking some medications, it may lead to a change in urine smell.

Especially the antibiotics that contain sulphonamide are known for causing odour in urine.

Other drugs that can alter the smell of urine include chemotherapy and this one for curing diabetes.

5. Water-Soluble Vitamin B

Vitamin B1 supplements (thiamine) and vitamin B6 (pyridoxine) can lead to pungent-smelling urine in babies.

So, if your baby is taking multivitamin supplements, that might explain the smelly wee.

That’s because vitamin B can’t be stored in the body. So any excess is eliminated in the urine.

This is true for supplements and food rich in vitamin B if consumed in large quantities, such as bananas, chicken, turkey, or salmon. 

6. Maple Syrup Urine Disease (MSUD)Why Does My Baby’s Urine Smell So Bad - babe in dreamland

Maple syrup urine disease is a very rare genetic disorder.

It affects the ability to break down and remove amino acids called leucine, isoleucine, and valine. As a result, these amino acids build up in the baby’s system and cause the urine and earwax to smell maple syrup.

This sweet smell is a typical symptom of MSUD and will emerge within the first days of a baby’s life.

MSUD can be potentially life-threatening if not diagnosed and treated early. However, this disorder is usually diagnosed through newborn screening programs.

Typically, newborn babies are subjected to blood screenings (heel prick tests) for inherited, rare conditions during their first days. And MSUD is one of them.

If your newborn is diagnosed with MSUD with the correct treatment the condition can be effectively managed, although it will never be cured.

7. Fish Odour Syndrome

Fish odour syndrome or trimethylaminuria is yet another rare genetic disorder. It causes unpleasant fish-like smelling urine. This odour results from the fact that the body cannot break down trimethylamine – a foul-smelling chemical produced by the digestive system into a non-fragrant chemical.

This leads to an accumulation of trimethylamine responsible for the odour in the baby’s sweat, urine, and breath.

That is the main symptom of this disease, and the baby appears to be healthy otherwise.

Again, there is no cure for this disease, but with the appropriate treatment, it can be managed, and the unpleasant smell – is significantly reduced.

Related post =======>? Why Does My Baby Have Smelly Armpits?

Final Few Lines

There are several possible reasons for unpleasantly smelling wee in babies. Often, they don’t necessarily mean that something is wrong with your baby, and you need to act on it.

Babies’ urine may smell abnormal due to the medication, vitamin B supplement your baby may be taking, or consuming some specific, fragrant foods.

However, other conditions should never be ignored and require medical attention.

Therefore, be aware of their symptoms and consult your doctor if you suspect urinary tract infection, dehydration, or rare genetic disorders such as maple syrup urine disease or fish odour syndrome.

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