What Causes Stammering?

Find out what we know so far about why people stammer.

There's evidence of people stammering throughout history. But it's only recently that we've started to find out what causes people to stammer. 

We don't yet know everything, but there are lots of things we do know.

Stammering myths

Firstly, let's get some of the falsehoods and misconceptions out of the way.

We know that people do not stammer because:

• they are nervous or anxious. 
• they have a certain personality type or level of intelligence. 

These judgements have been made about people who stammer since time began. But they're not true.

So why does it start?

The most common cause of stammering

Stammering usually starts in young children around the ages of 2 to 5. This is when they're going through rapid changes in their speech and language skills. We call this 'developmental stammering'.

Some children start stammering at a later age. This may be because language gets more complex. For example, sentences get longer and grammar gets more complicated.

Why does it happen?

We don't know exactly why stammering starts to happen. But research shows there's a slight difference in how the brain is wired in people who stammer.

We know stammering often has a genetic link, meaning it can run in families. Around 60% of people who stammer have a family member who stammers or used to stammer¹. 

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Don't blame yourself

We know that children do not start stammering because: 

• they were told off
• a new brother or sister joined the family 
• their parents separated.

So don't blame yourself. Nothing you have done as a parent or guardian has caused the stammering.

If a child starts stammering around the same time as events like these, it's coincidental. We know this because of the findings mentioned above.   

It also has nothing to do with your child learning or speaking more than one language. See Stammering & Bilingual Children for more information.

What else do we know?

Around the same number of boys and girls start stammering, roughly two boys to every one girl. 

However, girls are more likely to stop stammering. That means that men are more likely to stammer than women. Around 75% of people who stammer are male². Research continues to explore why this is.

We also know that stammering has nothing to do with where you are from. People of all ethnicities and from every country can stammer.

What to do

Has your child started stammering? See Help If Your Child Stammers if you're wondering what to do.

Or chat to us. Call our free helpline on 0808 802 0002 or start a webchat.

Other stammering causes

Stammering might start later for several different reasons. This is sometimes called 'acquired stammering'. 

If it starts in adults, it's often called 'adult onset stammering’ or 'late onset stammering'. 

It may change over time depending on what has caused it. 

Reasons that stammering can start, include:

1.    A returning stammer

Some adults may have stammered as a young child and stopped, but don't remember it. 

Or they may have a covert stammer that is so ingrained they don't see themselves as someone who stammers. But if their ways of coping begin to break down, they may find that they start stammering more.

2. Changes in the way the brain works

Sometimes the brain starts working in a different way. This can sometimes happen after a traumatic event. 

Or, prolonged psychological stress over time might cause stammering. It may also be associated with some psychiatric disorders. 

But quite often, there is no obvious explanation for why the brain has started working in a different way. 

Either way, this sort of stammering is sometimes called 'functional stammering'. Or 'functional neurological stammering' (FNS).

3. Changes in the physical structure of the brain

Sometimes stammering can start after receiving or developing:

• a head injury
• a brain tumour
• a stroke
• a degenerative disease such as Parkinson's
• some forms of dementia.

These might change the structure of the brain, resulting in stammering.

It is sometimes called 'neurological stammering' or 'neurogenic stammering'.

4. Medication and drug side effects 

Stammering can sometimes start as a side effect of taking medication or other drugs. 

5. Individual causes of stammering

Sometimes it may not be possible to find out what has caused a stammer that starts later. 

It might relate purely to the person concerned and does not fall into any of the above categories. This is sometimes called 'idiopathic stammering'.

What about streptococcal throat infections?

A recent piece of research has suggested that there's a link with a certain type of throat infection. The research found that 'streptococcal' throat infections may occasionally trigger stammering in children. 

The evidence base for this is still developing so we don't yet know for sure. But if your child has a streptococcal, or 'strep, infection, follow medical advice.

What to do

If you have started stammering and aren’t sure why, make an appointment with your GP to discuss the situation.

They can do some easy health checks and review any medications you might be on to rule out any worrying causes. 

Or chat to us. Call our free helpline on 0808 802 0002 or start a webchat.

Read more on our page Help if you have just started stammering.

More information & support

• What Is Stammering?
• Help For Your Stammer
• If You Don't Stammer Read This. Things we want you to know.
• Guides For Non-stammerers. Includes tips on speaking with people who stammer.

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