Know your breast density

It’s important for some people to know how dense their breasts are. Research shows that dense breast tissue is connected to a higher risk of breast cancer.

Only a breast screening mammogram can tell you if you have dense breasts. Breast density cannot be seen or felt in a clinical examination by a doctor.

What is breast density?

Breast density (‘mammographic density’) refers to how breasts look on a mammogram.

The types of tissue that make up the breast and can be seen on a mammogram are:  

• fatty tissue
• glandular tissue (the milk ducts and lobules)
• connective ('fibrous') tissue, which helps hold everything in place.

Breasts with a lot of glandular and connective tissue are described as ‘dense’ – they have ‘high mammographic density’.

Men tend to have less glandular and connective tissue in the breast than women. It’s not generally important for men to know their density level.

Understand the levels of breast density

When a radiologist reads a mammogram, they can give it a density score or scale.

There are different scales, but one of the most common is BI-RADS (the Breast Imaging Reporting and Data System from the American College of Radiology).

The BI-RADS system defines breast density in 4 categories – A, B, C, D (or sometimes 1, 2, 3, 4).

Type A – lowest density

Tissue is almost entirely fatty. Around 10% of women have mostly fatty, very low-density breasts. 

Type B – a low level of density

The breast has areas of fibrous and glandular (‘fibroglandular’) tissue. About 40% of women have this level.  

Type C – dense, may hide small cancers

Much of the breast is connective or glandular (‘heterogeneously dense’). Another 40% of women have this type of mammographic density.

Type D – the highest level, extremely dense

This level of density lowers how sensitive the mammography is. Tissue is mostly glandular/connective tissue. Around 10% of women have extremely dense breasts.

Most people have a density level somewhere in the middle of the 2 extremes, where the risk is not as high. 

What affects breast density

Several factors can change hormone levels in the body. This influences breast density to some extent.

The density level is mostly set when the breasts first form. Density usually due to a combination of age, hormone levels and a range of environmental influences.  

Breast size has no link to how dense your breast tissue appears on a mammogram.

Higher breast density

Mammographic density is likely to be higher in:

• young women
• women with a lower body mass index (BMI)
• women on hormone replacement therapy (HRT, also known as MHT)
• those with high-fat diet or high alcohol consumption
• women whose periods started at a young age or whose menopause started late
• women who have not had children.

Your genes are also important. You can inherit breast density, so people in the same family are likely to have similar level.

Lower breast density

Factors that can cause lower breast density include:

• having children
• going through menopause
• being on the hormone-blocking therapy Tamoxifen.

Ask about your breast density

BreastScreen currently tells people only in Western Australia and South Australia if their mammogram show dense breasts. BreastScreen will give you follow-up information and advise on any further investigation.

Later in 2025, we expect services in Victoria and New South Wales to report density to their clients. Queensland is currently conducting trials. Other BreastScreen services currently do not tell people about their mammographic density.

Some private screening clinics may give you this information but you may need to pay for a private mammogram. Talk to your GP if you are interested in this.

Don't be afraid to ask your doctor about your breast density. People have the right to know their density, their risks, and how sensitive a mammogram is at detecting cancers.

This can help you make informed decisions about screening and your own health.