If dairy leaves you feeling uncomfortable, you might wonder why your body cannot just “deal with it” like it used to. Lactose intolerance is common, and the most common reason is simple: your body is not making enough lactase, the enzyme that helps you digest lactose, the natural sugar in milk and dairy foods.
The empowering part is that understanding the “why” makes the “what now” much easier. Let’s break it down.
At a glance: the main reasons people are lactose intolerant
- Most lactase drop-offs fall into one of these buckets:
- Genetics (lactase nonpersistence): lactase naturally reduces after early childhood for many people.
- A gut issue or illness (secondary lactose intolerance): infection, coeliac disease, inflammatory bowel disease, or bowel injury can reduce lactase temporarily or longer-term.
- Rare genetic conditions: a very small number of people produce little to no lactase from birth (congenital lactase deficiency)
1) The most common reason: your genes switch lactase down over time
Most humans are born producing plenty of lactase because milk is a key food early in life. For many people, lactase production then gradually reduces after infancy and early childhood. This is called lactase nonpersistence, and it is the most common cause of lactose intolerance worldwide.
Why can some people digest milk forever?
Some people inherit genetic variants that keep lactase “switched on” into adulthood. That is called lactase persistence.
This is why lactose intolerance is not “random”. It is often a normal, genetically driven change over time.
2) Secondary lactose intolerance: when your gut needs time to recover
Sometimes lactose intolerance is not primarily genetic. It can happen when the lining of the small intestine is affected, which reduces lactase for a while.
Common causes include:
- Coeliac disease
- Inflammatory bowel disease
- Bowel infections
- Bowel surgery or injury
In these cases, lactose intolerance can improve if the underlying cause is treated and the gut lining recovers. If symptoms are new, changing quickly, or not clearly linked to dairy, it’s worth speaking to your GP.
3) Why lactose intolerance can show up at any age
Lactose intolerance can start at any age. That can happen because:
- Your genetically programmed lactase levels have gradually reduced and symptoms are now noticeable.
- Your gut is more sensitive due to illness, stress, or changes in routine.
- A gut infection or condition has temporarily lowered lactase (secondary lactose intolerance).
This is why people often describe it as “it used to be fine, and now it isn’t”.
4) The rare cause: when lactase is very low from the start
Congenital lactase deficiency is rare, but it does exist. Babies with this condition cannot break down lactose in breast milk or standard formula and can become unwell quickly without the right feeding plan.
What’s actually happening in your body when you have lactose intolerance?
When lactase is low, lactose is not fully broken down in the small intestine. It then passes into the large intestine where it can be fermented by gut bacteria, which can lead to symptoms like bloating, wind, cramps, and diarrhoea.
Symptoms commonly begin 30 minutes to 2 hours after having lactose, although this varies by person and what you ate.
What can help if you suspect lactose is the reason
You do not have to jump straight to cutting out all dairy. Many people find the most sustainable approach is about learning their personal tolerance and building a routine that feels comfortable.
A few practical steps:
- Notice patterns: a simple food and symptom diary for a week can be surprisingly helpful.
- Try smaller portions: symptoms often depend on the “lactose load”.
- Choose easier options: many people tolerate some dairy better than others (for example, yoghurt and cheese can feel different to milk).
- Get checked if symptoms persist: the NHS recommends seeing your GP if symptoms keep coming back, and notes tests like elimination diets or a hydrogen breath test may be used.
Where Milkaid fits in
Taking a lactase supplement before lactose-containing food or drink may reduce or prevent symptoms.
That is the role Milkaid is designed to play: supporting lactose digestion so you can enjoy dairy moments with more comfort and confidence.
Find out more information on our Instagram.