Medical Oncologist
CION Cancer Clinics
How NF1 is diagnosed, and what café-au-lait spots mean | CION Cancer Clinics
NF1 is usually diagnosed by examination, not a blood test. A doctor looks for signs from an agreed international list, such as café-au-lait spots, freckles in the armpits and small lumps along nerves. Two signs are needed, or one if a parent has NF1. This page explains each sign, why babies can be hard to diagnose, and when a gene test helps. At CION Cancer Clinics, our oncologists explain what a gene result means for you and your family, and plan the checks that follow.
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Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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On this page
- How do doctors decide whether someone has NF1?
- What are the signs on the NF1 checklist?
- Why is NF1 sometimes hard to confirm in a baby?
- What do the words in an NF1 assessment mean?
- Which skin spots point to NF1, and which usually do not?
- What this page cannot tell you
- Four things parents tell us, and what is actually true
- Common questions about diagnosing NF1
The short answer
How do doctors decide whether someone has NF1?
Mostly by looking, not by a blood test. A doctor checks the skin, the eyes and sometimes the bones against a list of agreed signs. A person whose parents do not have NF1 needs two or more of those signs. A child of a parent with NF1 needs only one.
Why a gene test is not always needed
The signs of NF1 are distinctive, and in most older children and adults the examination settles the question. A gene test is most useful when the signs are few or unclear, when a young child has only skin spots, or when a family wants the exact gene change for pregnancy planning.
Why the list was updated
An international expert group revised the criteria in 2021. They added the gene test itself as one sign, added a newer eye finding, and made room for Legius syndrome. That is a milder condition which causes similar skin spots but not the tumours of NF1, so telling the two apart matters for screening.
A few coffee-coloured spots on their own are common and do not mean NF1.What doctors look for
What are the signs on the NF1 checklist?
The revised list has seven items. They fall into four groups, and the doctor counts how many are present.
Skin signs
Flat, coffee-coloured patches called café-au-lait spots, and small freckles in places the sun does not reach.
- Six or more café-au-lait spots of a set minimum size
- Freckling in the armpits or groin
Lumps along nerves
Neurofibromas are soft, harmless growths on or under the skin. A plexiform neurofibroma is a larger one that grows along a nerve.
- Two or more neurofibromas of any kind
- Or a single plexiform neurofibroma
Eye signs
Found by an eye specialist using a slit lamp or a special scan.
- Two or more Lisch nodules on the iris
- Or two or more changes at the back of the eye
- A tumour of the nerve that carries vision
Bone and gene signs
Certain bone changes are typical of NF1, such as a bowed shin bone in a baby. A gene test showing a disease-causing change in NF1 in ordinary tissue, such as blood, now counts as a sign too.
Not sure whether this applies to you?
Ask an oncologistHow the signs appear
Why is NF1 sometimes hard to confirm in a baby?
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At birth and in infancy: spots appear first
Café-au-lait spots are often present at birth or appear in the first year. They may be the only sign for some time. A bowed lower leg, if present, is also usually seen early.
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Early childhood: freckling follows
Freckles in the armpits and groin usually appear a little later, in the toddler and preschool years. Once they do, many children meet the criteria.
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School years: the eye signs show up
Lisch nodules become more common as children grow. Yearly eye checks in early childhood also look for a tumour on the nerve that carries vision.
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Around puberty: skin lumps begin
Neurofibromas on the skin usually start to appear in the teenage years and increase in number through adult life.
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By the age of eight: most are clear
Nearly all children with NF1 meet the criteria by around eight. Until then, a child with spots alone is watched, or offered a gene test if the family wants an earlier answer.
On the clinic letter
What do the words in an NF1 assessment mean?
- Café-au-lait spot
- A flat, light-brown patch of skin, named after the colour of milky coffee. One or two are common in anyone.
- Axillary freckling
- Small freckles in the armpit. Similar freckles in the groin are called inguinal freckling.
- Lisch nodule
- A tiny, harmless raised spot on the coloured part of the eye. It does not affect sight.
- Optic pathway glioma
- A usually slow-growing tumour of the nerve that carries vision. Many never cause problems, but they are watched.
- Mosaic NF1
- NF1 signs limited to one part of the body, because the gene change arose after conception in only some cells.
- Legius syndrome
- A separate, milder condition caused by a different gene. It causes similar spots and freckles but not neurofibromas.
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Side by side
Which skin spots point to NF1, and which usually do not?
More suggestive of NF1
Usually not NF1
Six or more spots above the size threshold
One, two or three spots
Smooth, oval edges
Very jagged, map-like edges
Freckles in the armpits or groin as well
No freckling in the skin folds
A parent or sibling with NF1
No one in the family with similar signs
Being straight with you
What this page cannot tell you
It cannot tell you whether your child has NF1. Counting and measuring spots needs a trained eye, good light and sometimes a special lamp. Café-au-lait spots can be harder to see on darker skin, which is common in our patients. Photographs sent on WhatsApp are not enough to decide.
It cannot rule out other conditions
Several rarer conditions also cause coffee-coloured spots. One of them is linked to childhood cancers and is more likely where parents are related by blood. A doctor who knows these conditions will ask about the family and decide whether a gene test is needed to tell them apart.
Who this does not apply to
Most children with one or two café-au-lait spots do not have NF1 and need no tests at all. The same is true of an adult with a few spots and no other signs. A genetic counsellor or paediatrician is as ready to tell you that as to arrange a test.
What a gene result means for your child is a question for the counsellor who ordered the test.Commonly believed
Four things parents tell us, and what is actually true
"Birthmarks are just marks. They never mean anything."
Most do not. But six or more café-au-lait spots in a young child is worth showing to a doctor. Finding NF1 early means eye checks and blood pressure checks can start on time.
"Nobody in our family has NF1, so our child cannot have it."
About half of people with NF1 are the first in their family. The change happened for the first time in the egg or sperm. No one did anything to cause it.
"The spots will spread and turn into cancer."
Café-au-lait spots are harmless and do not become cancer. They are a marker that helps doctors recognise the condition. The health checks in NF1 are aimed at other parts of the body.
"If the gene test is normal, it cannot be NF1."
Testing finds a change in the large majority of people who meet the criteria, but not all. Mosaic NF1 can be missed in a blood sample. The diagnosis can still be made from the signs.
Questions we are asked
Common questions about diagnosing NF1
How many café-au-lait spots are too many?
The criteria count six or more spots above a set size, which is smaller for a child before puberty and larger after it. Fewer spots are common in the general population. Even six spots alone is only one sign, so the doctor looks for a second.
Which doctor should examine my child?
Start with a paediatrician or a skin specialist who sees NF1 regularly. They may refer you to an eye specialist for a slit-lamp check and to a genetic counsellor. In Hyderabad, several hospitals run combined clinics, so ask for one.
Does my child need a gene test to be diagnosed?
Not usually. If the signs are clear, the diagnosis is made on examination. A test helps when a young child has spots alone, when the signs are unusual, or when the family wants the exact change for future pregnancies.
Can NF1 be diagnosed in an adult?
Yes. Some adults, especially those with mild signs, are only diagnosed when their own child is. By adulthood the signs are usually clear. Tell the doctor about any lumps on the skin and any relatives with similar marks.
What is the difference between NF1 and Legius syndrome?
Both cause café-au-lait spots and freckling. Legius syndrome does not cause neurofibromas or the tumours linked to NF1, so it needs far less monitoring. In young children the two can look identical, which is when a gene test helps.
Is an MRI needed to diagnose NF1?
Not routinely. The diagnosis rests on the examination and, if needed, a gene test. An MRI is arranged when there are symptoms, such as a change in vision or a deep lump, that need a closer look.
My child has spots on only one side of the body. Is that NF1?
It may be mosaic NF1, where only some cells carry the change. It is usually milder. The chance of passing it on is lower, but a child who does inherit it has NF1 in every cell. A genetic counsellor can explain what this means.
Where do we start if we are worried?
Count the spots you can see and note any freckles in the armpits or groin. Take that, and any family history, to your paediatrician. Call the CION helpline if you are unsure who to see, and someone will point you to the right clinic.
Your Specialists
Meet CION's oncologists. Bring your family history or genetic report to them.
Our medical oncologists see people with a strong family history of cancer, arrange genetic counselling and testing where it fits, and plan the checks that follow.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
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Sources
- Genetics in Medicine — Revised diagnostic criteria for neurofibromatosis type 1 and Legius syndrome: an international consensus recommendation
- GeneReviews (NCBI) — Neurofibromatosis 1
- MedlinePlus Genetics — Neurofibromatosis type 1
- NHS — Neurofibromatosis type 1
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
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Worried about the spots on your child's skin?
Describe what you have noticed and any family history. We will tell you honestly whether an assessment is worth arranging, and who to see. One helpline serves every CION centre.