What Causes Dyslexia?

By Laura Lurns · Reviewed by Philip Weaver · Last reviewed 2026-10-01

Is there one cause?

The International Dyslexia Association (IDA) wrote a new definition in 2025. The definition describes trouble reading words or spelling, in accuracy, speed or both. It says the causes are complex. It names "genetic, neurobiological, and environmental influences" that act on each other as a child grows.

The definition names no single cause.

One paper describes the causes of conditions like dyslexia as "probabilistic and multifactorial" (Pennington, 2006). In that model, many things change the chances. No one thing decides alone. It is a model, not a study. We could read only its summary.

What might be underneath it?

The IDA's earlier definition was written in 2002. It said the trouble typically comes from a weakness in the sound part of language. It did not say it always does. For twenty-three years, people quoted it as if that word were not there. The 2025 definition says it openly. The IDA says trouble with word sounds and word parts is "common but not universal" in dyslexia.

It also says early spoken-language weak spots "often foreshadow" reading and writing trouble. That means they often come first. It does not say they cause it.

Our position, not the IDA's, is that reading draws on more than one system. In our view, a set of questions only about phonics will miss trouble elsewhere.

None of this is a reason to teach less phonics. Sounding out is the only way to handle a word a child has never seen. It does most of the work, most of the time.

What about genes?

The IDA's definition names genetic influences among the causes.

No study we hold can predict one child's dyslexia from family history.

Has anyone else in your family had trouble with reading or learning? If so, say so when you ask for help.

What about the brain?

The IDA's definition names "neurobiological" influences among the causes.

Catts and colleagues (2026) write that "no behavioral, genetic, or neurological correlate, beyond difficulties in word-level literacy, shows consistency at the individual level that is necessary to reliably identify dyslexia."

By their account, nothing beyond the reading and spelling trouble reliably identifies dyslexia in one child. No scan or gene test does. What is left to look at is the reading and the spelling themselves.

Can teaching or home life play a part?

We cannot tell you what caused it for your child. The IDA's 2025 definition names "environmental influences" among the causes. It does not say which ones.

Some things can look like dyslexia from across the table. Reading that was never taught step by step can look the same. If that is the only cause, the trouble is in the teaching, not the child. In our view, the teaching is the first thing to check.

Our page on whether it is dyslexia or something else covers the rest.

Is it about how smart they are, or how hard they try?

The 2025 definition sets no bar for how bright a child has to be.

The 2002 definition said the trouble was "often unexpected in relation to other cognitive abilities". The 2025 definition dropped that phrase. Catts and colleagues (2026) wrote the paper on the revision. They give the reason. Methods built on a gap between IQ and reading "lack predictive validity". That means they do not predict well.

To us, a child who avoids reading does not look like a child who is not trying. Calling it "lazy" only means the effort has not met the right method yet.

Does the cause change what you do?

In our view, the cause mostly does not change the first step. That step is to work out which job of reading is going wrong. The exception is a skill that was there and has gone. Our position is that a lost skill goes to a doctor first, not a tutor.

Our rule is to describe patterns on these pages. We do not put a name on a child. We say a child "is developing reading skills."

A diagnosis describes where a child is today. It does not predict where they will be after a year of the right kind of practice.

When to ask for help

Each of these is a reason to ask for help on its own.

• Little change, even with steady practice and good teaching.
• Reading well below what school expects.
• A teacher who raises a concern about reading.
• Extreme upset about reading.
• Complete avoidance of reading.
• Hopelessness about learning.
• Sadness or worry that lasts.
• Significant delays in speech, language or motor development.
• A skill that was there and has gone. Our position is that a lost skill goes to a doctor first, not a tutor.

Start with the teacher. Say what you are seeing at home, and what you have tried. Beyond the teacher, the right person depends on what it turns out to be about. If the work is too hard, someone who works on that school skill. If worry or mood is the thing, someone who works with children's mental health. In our view, delays in speech, language or movement are worth raising with your child's doctor. In our view, if you are worried enough to ask, a professional evaluation is worth asking about.

Any talk of hurting themselves is a same-day call to your doctor or a crisis line.