Dr Ayman Mahfouz

Armpit Lumps: Causes, Symptoms and How an Ultrasound Can Help with Diagnosis

February 25, 2023, 14:02 Breast, Ultrasound

Armpit lumps are a common occurrence for both men and women. They can range in size and have multiple causes. Finding a lump in your armpit can be alarming, but armpit lumps are not always a reason to worry. Many go away on their own.

You can put your mind at ease or make future treatment decisions once you know the nature of a lump in the armpit.

A quick, pain-free private Armpit / Axilla Ultrasound at Harley Street Ultrasound can give you the answers you need.

Symptoms of armpit lumps

An armpit lump may be as small as a pea, or it may be as large as a golf ball. It may feel soft or hard to the touch.

You may also notice that the spot where the lump is felt feels hot.

Other common symptoms of a lump in an armpit can include the following:

  • Lump grows larger when you’re very active, such as when exercising, but shrinks when you’re at rest

  • Pus – a thick, yellow or greenish discharge – emanating from the lump

  • Lump moves around slightly when pushed on

  • Pain when pressing on the lump

  • Fever or night sweats

  • Swollen lymph nodes anywhere in the body

It’s possible to experience several of these symptoms simultaneously.

Common causes of armpit lumps

Hair follicle problems

Nearly everyone has hair follicles under their arms. You can have a variety of problems with these follicles that cause an armpit lump. Some of the most common include:

  • Ingrown hairs – hairs (often itchy or irritated) stuck beneath the surface that can become aggravated by shaving, waxing, and deodorant use

  • Boils or carbuncles – abscesses caused by


    Staphylococcus aureus


    bacteria in the follicle

  • Cysts that form around hair follicles

  • Folliculitis – inflammation of the follicle resembling acne

  • Hidradenitis suppurativa – a chronic inflammatory skin condition where skin rubs against skin

Skin issues

When your skin gets irritated, it can result in a lump under the arm. Shaving can irritate the skin, as can chafing from sports or working in hot weather. Impetigo is a common skin condition caused by Staphylococcus bacteria that produces a rash and blisters.

Also known as acrochordons, skin tags form where the skin rubs against itself, including in the armpit. Some skin tags can grow to be as large as a few centimetres in size, making them feel like a lump in the armpit.

Lipomas are fatty tissue just beneath the skin. These growths are mostly harmless but can be irritating and unsightly.


Injury to the armpit area can cause a lump to form. Whether you have overstretched or had a trauma to the armpit, you may develop an armpit lump. A blow in contact sports, a car accident, or similar incident may be the culprit.

Allergic reaction

An allergic reaction can cause a lump in the armpit. Most likely, it’s something external that has irritated the skin. However, allergic reactions can also manifest from the inside out, leaving you with a lump under your arm.

Bacterial, viral or fungal infection

We’ve already mentioned some infection possibilities associated with the hair follicles behind armpit lumps. But many other types of bacteria, viruses, and fungi can provoke a lump under the arm.

Most commonly, the influenza virus (the flu) and mononucleosis caused by the Epstein-Barr virus are to blame. The flu typically circulates more during winter months when people are indoors, and some years have worse strains than others.

Many infections will also cause swollen lymph nodes. You have clusters of lymph nodes throughout the body, including under the arms. They contain immune cells to fight infection and therefore become swollen when actively working to fight off bacteria and viruses.

Post-vaccination reaction

Have you had a vaccine recently? Some people get an armpit lump temporarily after receiving a vaccine, including the COVID-19 vaccine. This is your body’s response to the vaccine, as your immune system is being triggered to fight future infection.

Benign and cancerous tumours

While a lump under the arm could possibly be cancer, there are many, many types of tumours that could also account for the lump, many of them benign (harmless). For example, fibroadenomas are benign breast lumps that can be felt in the armpit. Many don’t even require treatment, only monitoring.

There are more serious kinds of tumours, though, including soft tissue sarcomas and breast cancer, that can also form a lump in the armpit. That’s why it’s important to follow up with a diagnosis, starting with an ultrasound. If needed, a biopsy can be performed for more information.

Leukaemia or lymphoma

Leukaemia is a form of cancer of the blood that begins with a rogue cell in the bone marrow and affects the white blood cells of your immune system. It can sometimes present as an armpit lump, as can lymphoma.

Lymphoma is a cancer of the lymph system. There are many types of lymphoma, requiring different treatments and carrying very different prognoses.

Systemic lupus erythematosus

Lupus is a chronic autoimmune disease where the body attacks its own tissues. It causes inflammation – sometimes localised and sometimes widespread over the body – and hence may result in an armpit lump.

How an ultrasound helps with the diagnosis of a lump in your armpit

Also known as sonography, ultrasound uses sound waves to create an image of what’s in your body. A transducer that looks a little like a small microphone sends the sound waves beneath the skin and also records the waves that are echoed back.

Sound waves react differently to various types of tissue and are consequently reflected back in a unique way to give an image. You’ve probably seen these images of babies before they were born and know how accurate they are.

An ultrasound can usually detect the difference between different types of tumours based on their characteristics and how they respond to sound waves. It can also tell the difference between a cyst and a tumour, for instance.

If you’re worried about an armpit lump, an ultrasound is a good place to start investigating. We will let you know if we think a biopsy or another type of follow-up is recommended.

What to expect during and after your ultrasound for an armpit

Ultrasounds are a preferred first step in diagnosing many armpit lumps because they are noninvasive and painless. At Harley Street Ultrasound, a medical doctor who is a specialist will perform your ultrasound.

At your appointment, a clear, hypoallergenic, water-based gel is applied under the arm. This helps the transducer get better images during the ultrasound test, and it helps it glide better over your skin for greater comfort. It may feel cool for a few seconds, but most patients hardly notice it.

You may be asked to move your arm slightly for the best position to obtain clear images. The whole process usually takes less than an hour. Your doctor will let you know the findings right away, and we aim to have a report and images for you on the same day.

There’s no downtime required afterwards, so you can go about your day normally, whether that’s work, school or home activities.

When to schedule an ultrasound for a lump in your armpit

You can schedule an ultrasound for an armpit lump any time with Harley Street Ultrasound for your own peace of mind. That’s the advantage of going to a private ultrasound service; there’s no waiting for a referral or for NHS approval.

You get same-day results at Harley Street Ultrasound, so you know if you don’t need treatment or if you should follow up with another physician. Getting an ultrasound at Harley Street Ultrasound will not keep you from continuing care with your regular NHS provider.

When it comes to armpit lumps, we recommend either seeing your physician or scheduling an ultrasound as soon as possible if:

  • You have an armpit lump that lasts longer than two weeks.

  • The lump grows bigger.

  • You have had a lump removed and it grows back.

  • The symptoms of your armpit lump are getting worse, such as the pain is increasing.

  • You have pain accompanying your armpit lump.

  • You have a fever or another sign of infection.

We understand it can be hard these days to see your normal medical provider and that getting an ultrasound can help when you would otherwise wait weeks to see someone.

To schedule your ultrasound for an armpit lump, you can ring Harley Street Ultrasound on 0203 904 4441, or book online.

Still have questions? We’re happy to answer them on the phone, or feel free to reach out via our contact form and let us know how we can help you.

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