What is cervical intraepithelial neoplasia (CIN)?

Cervical intraepithelial neoplasia (CIN) is a term that describes abnormal changes of the cells that line the cervix. CIN is not cancer. But if the abnormal cells are not treated, over time they may develop into cancer of the cervix (cervical cancer).

CIN does not cause any symptoms. You are not likely to find out you have it unless you have cervical screening. Screening uses tests to find abnormal changes and to check whether they should be treated.

For some people with CIN, the abnormal changes go back to normal naturally. But if you do need treatment, it is usually very effective. Treatment removes or destroys the abnormal cells and prevents cancer developing in the future.

Causes of CIN


The main cause of CIN is an infection called the human papilloma virus (HPV). There are over 100 types of this virus. Some types of HPV can affect the cervix. The types that cause abnormal cell changes in the cervix are called high-risk HPV

Usually, the body’s immune system gets rid of the infection naturally. There are no symptoms and often the virus does not cause damage. Most people will never know they had it.

In some people, the immune system does not get rid of the infection and the virus stays in the body for longer. We do not know exactly why this is. If the cervix is affected by HPV for a long time, the virus can cause damage that may eventually develop into CIN.

HPV is very common, and most people are infected with it at some point. It can affect all sexual orientations and anyone who has ever been sexually active. This includes people in a long-term relationship with one partner. HPV may still affect you even if you have not been sexually active for some years. 

The virus can live on the skin around the whole genital area. It passes easily from person to person during any type of sexual contact, including skin-to-skin genital contact or sharing sex toys. Using a condom or other barrier contraception may reduce your risk of HPV infection, but it does not offer complete protection.


Your risk of developing CIN is higher if you smoke. This may be because:

  • smoking makes your immune system less effective at getting rid of HPV
  • the chemicals in tobacco can damage your cells.

If you want to stop smoking:

Signs and symptoms of CIN

CIN and HPV do not cause any symptoms. It is important to have regular cervical screening tests to check for abnormal cell changes. If needed, these changes can be treated to prevent cancer.

Diagnosing CIN

The first part of cervical screening is a smear test. This does not show if you have CIN. But if your test result shows abnormal cells, you may then have a test called a colposcopy.

The colposcopy shows abnormal areas of the cervix and how abnormal the cells are. It can be used to diagnose CIN and to decide if you need treatment.


CIN 1 means one-third of the thickness of the cervical surface layer is affected by abnormal cells. This will often return to normal without any treatment at all. You will have further cervical smear tests or colposcopies to check the cells have improved. If these tests show the CIN 1 is not improving, you may be offered treatment.


CIN 2 means two-thirds of the thickness of the cervical surface layer is affected by abnormal cells. There is a higher risk the abnormal cells will develop into cervical cancer. You may be offered treatment to stop this happening, or another colposcopy.


CIN 3 means the full thickness of the cervical surface layer is affected by abnormal cells. CIN 3 is also called carcinoma-in-situ. This sounds like cancer, but CIN 3 is not cervical cancer. Cancer develops when the deeper layers of the cervix are affected by abnormal cells. You will be offered treatment to stop this happening.

Treating CIN

There are different types of treatment that can be used to remove CIN. Your doctor will explain what treatment they suggest for you. They will only offer treatment if they are sure the cells are very abnormal and there is a risk of cancer developing. You usually only need one treatment to remove the abnormal cells completely.

You may have one of the following:

  • Treatment during your colposcopy test

    Sometimes the doctor or nurse can see that the cells are very abnormal during the colposcopy. They may offer you treatment to remove these cells straight away during the test.

  • Treatment at a later appointment

    Sometimes the colposcopy shows abnormal cells, but it is not clear how serious the changes are. The doctor or nurse will collect a small sample (biopsy) of the cells to check under a microscope. They will contact you with the results. They will give you another appointment if you need treatment.

Making treatment decisions

Before any treatment, you should be given time and information to make a decision about your treatment. If you have questions, or are not sure, the treatment can always be done another day.

Follow-up for CIN

Treatments for CIN are usually very successful. To check, you will be asked to have another cervical smear test about 6 months after your treatment. Your sample will be carefully checked for signs of abnormal cells and for high-risk HPV. What happens next depends on the results:

  • If the sample shows no HPV
    You will be asked to have cervical screening again in 3 years. Your risk of developing more serious abnormal changes in this time is very low.
  • If the sample shows HPV
    You will be asked to have another more detailed check-up, with a colposcopy.

Sometimes the colposcopy shows that an abnormal area of cells has come back and more treatment is needed. This does not happen often. The same types of treatment can often be used again to remove or destroy the abnormal area of cells.

Very occasionally, if the abnormal cells keep coming back after treatment, your doctor might suggest having surgery to remove the cervix completely. This usually means having an operation called a hysterectomy. Your doctor will explain if they think this is right for you.

After a hysterectomy, you may still need tests to check for abnormal cells. This is similar to having a cervical smear test, but the sample of cells is taken from the top of the vagina. It is sometimes called a vaginal vault smear.

Your feelings

Finding out you are affected by CIN can be stressful and hard to cope with. The tests and treatments used for CIN are very personal. You may find it a bit embarrassing. For some, the thought of having procedures is frightening and stressful.

It may help to remember that the aim is to stop cancer before it develops. Treating a small area of abnormal cells is usually a simple and effective way to do this.

You are likely to need several appointments to treat CIN and then check how effective treatment has been. You may feel anxious waiting for the next appointment, treatment or more test results.

You may feel ashamed or embarrassed about CIN. It is natural to have mixed emotions, including feeling uncertain or alone. You may have questions or worry what others will think.

If you are finding it hard to cope, it may help to talk about it with someone:

  • You could talk to a family member or friend.
  • Your GP or practice nurse can answer any questions you have and explain how they can support you. 
  • You might find it is easier to talk online to people in a similar situation. Our Online Community offers this kind of support. 
  • You can call one of our cancer support specialists on 0808 808 00 00 (7 days a week, 8am-8pm).

About our information

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Professor Nick Reed, Consultant Clinical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

  • use plain English
  • explain medical words
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We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

Date reviewed

Reviewed: 01 April 2021
Next review: 01 April 2024

This content is currently being reviewed. New information will be coming soon.

Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.