Poop is a big part of parenthood, especially in those newborn and infant days. (Nod “yes” if you’re elbow deep in dirty diapers!)

You may even be startled at what you find sometimes. Different colors, consistencies, and — gulp — even blood or mucus. You’re in good company, though. The good news is that most poop you see — even the really weird-looking stuff — can be totally normal.

There are a few times when you may have reason for concern, however. Take lactose, for example. It’s a sugar that’s found in both breast milk and formula. While very rare, some babies are intolerant to lactose because their bodies lack the enzyme (lactase) that digests it. With intolerance comes watery, loose stools and other digestive issues.

But loose stools can mean other things, too. So how can you tell the difference between lactose intolerance and more common issues? Let’s take a closer look.

Related: What does your baby’s poop color say about their health?

It’s important to understand that lactose intolerance is really uncommon in children under ages 2 to 3 years old. In fact, it tends to appear more often in adolescents and adults, when it’s usually known as primary lactose intolerance.

People with this condition begin life with a good supply of lactase, the enzyme that breaks down lactose. As they get older, their lactase levels may decrease dramatically and make digesting even small amounts of milk products difficult.

Primary lactase deficiency impacts up to 70 percent of people and is determined in part by genetics. It also happens to be more common in individuals of Asian, African, Hispanic, American Indian, Mediterranean, and Southern European descent. Not all people with lactase deficiency will have symptoms.

Congenital lactose intolerance

This isn’t to say that babies can’t be born with lactose intolerance. This condition is called congenital lactose intolerance, and it’s passed down genetically — in families — through what’s called autosomal recessive inheritance. This means that a baby has received the gene from both the mother and father at conception.

In a way, it’s like winning the genetic lottery, and studies consistently report that lactose intolerance is extremely rare in babies.

Infants with congenital lactose intolerance show signs right away, with the first few feedings up to 10 days old. Symptoms, like watery diarrhea, don’t take much time to develop because — unlike with primary lactose intolerance — the enzyme lactase is either deficient or simply absent from birth. You may also see this condition called:

  • alactasia
  • hypolactasia
  • lactose malabsorption
  • milk sugar intolerance
  • congenital lactase deficiency

Galactosemia is another congenital condition that isn’t lactose intolerance, but may similarly affect your baby’s ability to process lactose in formula or breastmilk.

It’s a rare metabolic condition where the body either doesn’t produce any or doesn’t produce enough GALT, the liver enzyme needed to break down galactose.

Galactose is a part of the lactose sugar, but having galactosemia isn’t the same thing as being lactose intolerant. With this condition, babies may have similar symptoms, however, like diarrhea. These symptoms generally appear within a few days after birth.

Galactosemia can be life-threatening if not detected early. Fortunately, the most common form is part of the standard newborn screen done in the United States.

Developmental lactose intolerance

Developmental lactose intolerance is also present at birth. It’s a result of a baby being born prematurely (before 34 weeks’ gestation). Babies born early may have lower lactase levels because this enzyme is typically produced late in the third trimester.

This form of intolerance may not last terribly long. Babies may quickly outgrow it as their small intestine matures.

Secondary lactose intolerance

Secondary lactose intolerance can affect babies, children, and adults. With this form, the small intestine lowers its lactase production in response to illness or injury.

Common offenders include things like Crohn’s disease, celiac disease, and bacterial overgrowths. With babies, this intolerance may develop after a bought of severe diarrhea, malnutrition, or other illness.

With time, the body may be able to process lactose after receiving treatment for the underlying condition.

Related: Everything you need to know about lactose intolerance

Again, signs and symptoms of lactose intolerance in babies usually begin within a few days after birth. If your baby is fine for several months and then shows these signs, the culprit is likely not lactose intolerance — unless your little one’s been ill and develops the secondary form.

Symptoms include:

  • diarrhea
  • bloating, gas, and nausea
  • abdominal pain and cramping
  • malnutrition/failure to thrive

Since babies can’t tell you what’s bothering them, you may notice your baby is fussy or crying after feedings. Their abdomen may be swollen or firm. They may also cry when passing gas or pooping.

Diaper contents may be the clearest indicator here. Your baby’s stools may be loose and watery. They may also appear bulky or frothy. They can even be acidic, which means you may notice diaper rash from your baby’s skin becoming irritated. (Ouch!)

It’s important to speak with your doctor to receive a correct diagnosis before changing formula or trying other treatments.

The rare baby with congenital lactose intolerance should be given a lactose-free formula. Without making this switch, babies may experience weight loss and dehydration. This condition can even be life-threatening if not treated promptly.

Once your baby is old enough to eat food, try focusing on calcium-rich foods to bridge that nutrition gap. These include foods like:

  • broccoli
  • pinto beans
  • calcium-fortified soy or other milk substitutes
  • calcium-fortified breads and juices
  • spinach

You may also want to talk to your pediatrician about supplements to support your baby’s vitamin D levels.

There are a few other possibilities for your baby’s strange diapers. Check in with your pediatrician to make an accurate diagnosis and treatment plan.

Milk allergy

Some babies may be allergic to cow’s milk — it’s actually one of the morecommon food allergies among children, though it is less common in younger infants.

After drinking milk, the immune system responds, causing a range of symptoms from mild to severe. This might include things like:

  • wheezing
  • throwing up
  • getting a skin rash or hives
  • having tummy troubles

Your baby may experience bouts of diarrhea or loose stools with or without blood.

Many children outgrow a milk allergy in time. Otherwise, treatment is simply avoiding formula and other foods containing milk from cows and other mammals.

There is a small risk of anaphylaxis with milk allergy, so it’s truly key to determine if your child is intolerant or allergic.

Cow milk protein intolerance

Some babies have trouble breaking down the proteins in cow’s milk. If your little one is sensitive to milk proteins, you may see diarrhea — even bloody diarrhea — and mucus in the stool. Your baby may also experience a rash, eczema, abdominal pain, or vomiting.

Symptoms of this intolerance tend to develop within the first week of exposure. This condition affects formula-fed babies, but milk proteins can also pass through breastmilk if a mother consumes dairy.

Some 2 to 5 percent of babies have this sensitivity, but it generally resolves by the time they reach their first birthdays. So an ice cream cake may still be an option for the big day. Ready the camera!

Foremilk/hindmilk imbalance

If you breastfeed, you may have heard that your milk is divided into two types. Foremilk may be lighter, like skim milk. Hindmilk may appear fattier, like whole milk. More foremilk is produced at the start of a nursing session. The more time your baby nurses, the more hindmilk they’ll get.

With some babies, if there’s an imbalance and baby gets too much foremilk, it may cause anything from gas to irritability. Your baby’s poop may be explosive at times. And it can look green, watery, or foamy.

Related: Does my baby have a foremilk/hindmilk imbalance?

You may want to switch formulas with the guidance of your doctor if your child is allergic to milk or if they show a protein sensitivity. There are a variety of choices on the market, including soy and hypoallergenic formulas that you can purchase both over the counter and by prescription.

Breastfeeding mamas may need to modify their own diets to ensure that milk and its protein isn’t passed through down to their baby. This means avoiding obvious foods like milk, cheese, yogurt, and other dairy products.

You’ll also need to read labels carefully to look for things like dry milk solids, buttermilk, casein, and other products found in processed foods. Talk to your doctor before following any strict elimination diet, as you may be missing out on important nutrients.

If you suspect foremilk/hindmilk imbalance, a visit to a certified lactation consultant may be helpful. You may want to try feeding more frequently or feeding baby fully on one breast before changing to the next.

Related: Milk protein allergy: What are my formula options?

Poop of all colors and textures may be normal in babies. If weird-looking poop is accompanied by excessive crying, gas, blood in the stool or other symptoms, visit your pediatrician.

Lactose intolerance is rare in infants, but there are a range of other conditions and situations that may require switching formulas or trying different feeding methods to make baby happier and healthier.