The symptoms of lactose intolerance will usually occur within a few hours of consuming food or drink that contains lactose, such as dairy products.

The main symptoms include:

• flatulence (wind)
• diarrhoea
• bloated stomach
• stomach cramps and pains
• stomach rumbling
• feeling sick

The severity of your symptoms and exactly when you begin to experience them will depend on the amount of lactose that you have consumed.

The amount of lactose that it takes to cause your symptoms will vary from person to person. For example, some people may still be able to drink a small glass of milk without triggering any symptoms, while others may not even be able to have milk in their tea or coffee.

Seeking medical advice

The symptoms of lactose intolerance can be similar to those of other conditions, so it's important to see a GP for a medical diagnosis if you think you or your child may be lactose intolerant.

For example, the symptoms above can also be caused by:

• irritable bowel syndrome (IBS) – a long-term disorder that affects the digestive system
• milk protein intolerance – an adverse reaction to the protein in milk from cows (not the same as a milk allergy)  

Read more about diagnosing lactose intolerance.

Allergy

Allergy is the term used to describe an adverse (bad) reaction that the body has to a particular substance.

Immune system

The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.