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What Causes Hard Forearm Lumps & When to Seek Care

A forearm diagonal from the top left to the bottom right. A lump is towards the elbow with red concentric circles emanating from it.
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Hard, small bumps on the forearm are most commonly caused by skin conditions that form cysts, warts, or abscess. A hard, painful lump on the forearm can be caused by trauma from an injury, or even an insect bite. Other less common causes include fatty tissue growth that forms a hard lump under the skin of the forearm. Learn more below about other causes and treatment options.

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Hard lump on forearm explained

The forearm is a complex part of the body, allowing you to twist your arm during a tennis match or reach for your phone at work. A lump in this area can be concerning; however, there are many benign causes associated with this symptom.

Forearm structure

The forearm is defined by the area in the upper limb between the elbow and wrist. The long bones of the forearm are called the radius and the ulna. It contains an anterior group of muscles that help flex the wrist and fingers and a posterior group of muscles that help extend the wrist and fingers. There are three primary nerves that run through the forearm called the radial, median and ulnar nerve, and two principal arteries in the forearm called the radial artery and ulnar artery.

Now that the normal structural characteristics have been detailed above, we can look into some possible characteristics of your hard forearm lump.

Common accompanying symptoms of a hard forearm lump

If you have a hard forearm lump, you may also experience:

  • Pain or discomfort
  • Tenderness to the touch
  • Redness
  • Blistering
  • Itching

Less-concerning characteristics

New lumps and bumps on the body are also concerning since they can be the initial sign of a cancerous process. However, there are signs and symptoms that are reassuring. Lumps in the forearm are less concerning if they have the following characteristics:

  • Soft
  • Easily mobile

Concerning characteristics

Lumps in the forearm that require care have the following characteristics:

  • Hard
  • Rigid/stuck in place
  • Grows in size over time
  • Changes in color

Make an appointment with your physician if you experience these symptoms in order to get appropriate treatment.

What causes a lump on the forearm?

Any disease, damage, or injury to the structures of the forearm can result in a hard forearm lump. In addition to the muscles, nerves, and bones of the forearm, there are also various tendons, tissues, ligaments, and arteries throughout this area that can also cause lumps. Conditions can be most easily categorized as benign (noncancerous) or malignant (cancerous). The following details may help you better understand your symptoms; however, you should see a physician for a proper diagnosis.

Benign causes

There are various benign causes behind a forearm lump, including:

  • Growths: Growths can occur in the muscle, soft tissue, and nerves of the forearm causing hard, sometimes large lumps. For example, a growth of nerves in the forearm can result in lumps as well as symptoms of pain or numbness.
  • Dermatologic: There are many dermatologic conditions that can result in a hard lump in the forearm. For example, cysts are sacs that can be filled with fluid, air, or other material and can form in any part of the body. Cysts can occur in the forearm, causing pain or possible injury from inflammation.
  • Inflammatory: This includes conditions such as infections, panniculitis, and even arthritis, which can result in multiple bumps in the forearm that can be red, fairly tender or painful. Panniculitis is a group of inflammatory diseases that affect the fatty tissue under the skin and result in skin nodules. Arthritis is a general term for multiple conditions that cause painful inflammation and stiffness throughout the body. Arthritis can result in thickening and swelling that can result in damage and deformity of the bones and cartilage in the form of nodules. See this image for a visual representation of arthritic nodules.
  • Traumatic: Trauma to the forearm area from bumping a table, falling, or being in an accident can result in forearm lumps. Traumatic causes may also involve visible deformity or bleeding, depending on the severity of the trauma.
  • Environmental: Insects are a nuisance in general, and are even more annoying when they bite you. A bite from any insect, such as a mosquito, spider, flea, etc., can cause a hard lump on the forearm that can also swell and become itchy and painful.

Malignant causes

In general, any growth is the result of cells dividing and growing uncontrollably. Sometimes there is a genetic mutation in DNA or a specific protein that results in this unchecked growth. These abnormal cells accumulate to form a noticeable lump. A lump (also known as a tumor) can be benign and can arise from many of the causes above. However, if this lump grows and invades the body, it is considered malignant. For example, a rare type of cancer called sarcoma originates in the supportive, connective tissues of the body and can result in a hard forearm lump before or as it spreads.

This list does not constitute medical advice and may not accurately represent what you have.

Skin abscess

A skin abscess is a large pocket of pus that has formed just beneath the skin. It is caused by bacteria getting under the skin, usually through a small cut or scratch, and beginning to multiply. The body fights the invasion with white blood cells, which kill some of the infected tissue but form pus within the cavity that remains.

Symptoms include a large, red, swollen, painful lump of pus anywhere on the body beneath the skin. There may be fever, chills, and body aches from the infection.

If not treated, there is the risk of an abscess enlarging, spreading, and causing serious illness.

Diagnosis is made through physical examination.

A small abscess may heal on its own, through the body's immune system. But some will need to be drained or lanced in a medical provider's office so that the pus can be cleaned out. Antibiotics are usually prescribed.

Keeping the skin clean, and using only clean clothes and towels, will help to make sure that the abscess does not recur.

Rarity: Common

Top Symptoms: rash with bumps or blisters, red rash, red skin bump larger than 1/2 cm in diameter, pus-filled rash, rash

Symptoms that always occur with skin abscess: rash with bumps or blisters

Urgency: Primary care doctor

Skin cyst

A cyst is a small sac or lump, filled with fluid, air, fat, or other material, that begins to grow somewhere in the body for no apparent reason. A skin cyst is one that forms just beneath the skin.

It's believed that skin cysts form around trapped keratin cells – the cells that form the relatively tough outer layer of the skin.

These cysts are not contagious.

Anyone can get a skin cyst, but they are most common in those who are over age 18, have acne, or have injured the skin.

Symptoms include the appearance of a small, rounded lump under the skin. Cysts are normally painless unless infected, when they will be reddened and sore and contain pus.

Diagnosis is made through physical examination. A small cyst can be left alone, though if it is unsightly or large enough to interfere with movement it can be removed in a simple procedure done in a doctor's office. An infected cyst must be treated so that the infection does not spread.

Rarity: Common

Top Symptoms: skin-colored armpit bump, marble sized armpit lump, small armpit lump

Symptoms that always occur with skin cyst: skin-colored armpit bump

Urgency: Wait and watch

Severe skin abscess

A skin abscess is an infection of the deeper skin that's typically due to bacteria seen on the skin. Recently, infections are more frequently caused by Staph. Aureus (puts the "staph" in "staph infections"). If the infection begins to spread, urgent treatment is required.

You should head to the nearest ER by car since your infection seems like it might be spreading. It is likely that you will be prescribed antibiotics. Surgery may be required to get rid of the whole abscess after the inflammation has died down. Do not drain the abscess yourself.

Rarity: Rare

Top Symptoms: fatigue, fever, painful neck lump, marble-size neck lump, pink or red neck bump

Symptoms that always occur with severe skin abscess: pink or red neck bump, red bump

Urgency: Hospital emergency room


Melanoma is the most serious type of skin cancer. Often the first sign of melanoma is a change in the size, shape, color, or feel of a mole. Most s have a black or black-blue area. Melanoma may also appear as a new mole. It may be black, abnormal, or "ugly looking."

You should visit your primary care physician. Surgery is the first treatment of all stages of melanoma. Other treatments include chemotherapy and radiation, biologic, and targeted therapies. Biologic therapy boosts your body's own ability to fight cancer. Targeted therapy uses substances that attack cancer cells without harming normal cells.

Rarity: Rare

Top Symptoms: brown-colored skin changes, atypical features of a facial bump, black-colored skin changes, growing facial lump, large facial lump

Symptoms that always occur with melanoma: atypical features of a facial bump

Urgency: Primary care doctor


Lipoma is a word that translates as "fatty tumor," but a lipoma is not cancer. It is simply a growth of fat between the muscle layer and the skin above it.

The exact cause is not known. The condition does run in families and is associated with other unusual syndromes such as adiposis dolorosa, which is similar. Lipomas most often appear after age 40.

Symptoms include a soft, easily moveable lump beneath the skin, about two inches across. A lipoma is painless unless its growth is irritating the nerves around it. They are most often found on the back, neck, and abdomen, and sometimes the arms and upper legs.

It is a good idea to have any new or unusual growth checked by a medical provider, just to make certain it is benign.

Diagnosis is made through physical examination, biopsy, and imaging such as ultrasound or CT scan.

Most of the time, treatment is not necessary unless the lipoma is unsightly or is interfering with other structures. It can be removed through surgery or liposuction.

Rarity: Uncommon

Top Symptoms: skin-colored groin bump, marble sized groin lump, small groin lump

Symptoms that always occur with lipoma: skin-colored groin bump

Urgency: Wait and watch

Insect bite on the arm

Insect bites are very common. They often cause itchiness, redness, and some swelling. Most insect bites can be treated at home.

Rarity: Common

Top Symptoms: swollen forearm, mild forearm pain, forearm bump, forearm redness, forearm itch

Symptoms that never occur with insect bite on the arm: fever, worsening forearm redness, severe forearm pain, high-pitched breathing, wheezing, racing heart beat

Urgency: Self-treatment

Forearm wart

Warts, also called common warts or verrucae, are small, rough, rounded growths on the top layer of the skin. They may appear singly or in clusters.

Common warts are caused by the human papilloma virus (HPV) and are contagious through direct contact, especially through a break in the skin. They may spread from one place on the body to another simply through touch.

Anyone can get warts but they are most common in anyone with a weakened immune system, as from illness or chemotherapy. Children and teenagers are also susceptible to warts.

Warts often first appear on the hands and fingers, especially near the nails or after any injury to the skin. This is why biting fingernails is a risk factor for warts.

Warts are benign, meaning they are not cancerous. But they can be unsightly and interfere with normal use of the hands, so treatment is often beneficial.

Diagnosis is made through physical examination. Warts in children sometimes go away without treatment, but otherwise most warts can be easily removed in a doctor's office.

Rarity: Common

Top Symptoms: skin-colored forearm bump, painless forearm lump, small forearm lump, scaly forearm bump

Urgency: Self-treatment


A dermatofibroma is a fairly common skin growth that usually appears on the lower legs, but may appear anywhere on the body. These mole-like growths are benign (noncancerous.)

The cause is not known, though a dermatofibroma may appear after a minor injury. The growths are not contagious.

Dermatofibromas are most common in adults and are rarely found in children.

Symptoms include a hard, raised growth that is red, pink, or brown and less than half an inch across. They are usually painless but may be tender or itchy, and may appear alone or in groups.

Any new growth on the skin should be seen by a medical provider, especially if the growth is very dark in color or changes its shape or appearance quickly.

Diagnosis is made through physical examination and sometimes biopsy.

A dermatofibroma does not require treatment unless it is interfering with clothing or is unsightly. They can be surgically removed, though this will leave a scar and the growth may eventually return.

Basal cell carcinoma

Basal cell carcinoma (BCC) is the most common kind of skin cancer. It can develop almost anywhere on the body. It appears as abnormal spots or bumps on the skin. These bumps are often pink, red, or skin-colored and sometimes have a shiny surface. The main risk factor for developing this condition is prolonged exposure to ultraviolet (UV) radiation. Sun exposure and tanning beds are both sources of UV radiation. People with a history of sunburns, previous skin cancer, and a weakened immune system are at higher risk for this condition.

Most cases of BCC can be easily treated because they grow slowly. Though if not treated, it can spread inside the body. Your provider will do a skin exam and possibly skin sample test, known as a biopsy. Treatment will depend on where the cancer is, its size, and your medical history. Some treatment options include cutting out the bump, freezing it, or using medicated skin cream.

Rarity: Uncommon

Top Symptoms: facial skin changes, pink or red facial bump, small facial lump, painless facial bump, growing facial lump

Urgency: Primary care doctor

When to seek treatment for a hard lump on the forearm

Since the causes of forearm lumps are varied, it is important to make an appointment with your physician in order to get the proper diagnosis and treatment.

Medical treatments

Depending on the cause of your symptoms, your physician may suggest the following.

  • Surgery: Surgery is often the first option for removing both benign and malignant growths from the forearm and other areas of the body. Surgery for malignant growths is also often combined with other chemical treatments.
  • Pain medication: Medications such as NSAIDs (non-steroidal anti-inflammatory agents) that help alleviate the pain associated with forearm lumps are often used to help treat this condition. Common NSAIDs include ibuprofen (Advil, Motrin) and naproxen (Aleve).
  • Anti-inflammatory: Inflammatory causes of forearm lumps may be treated with various types of medications that target and decrease inflammation, such as immune system-suppressing drugs (immunosuppressants).
  • Cancer treatment: If your forearm lump and associated symptoms are due to malignant cancer, your physician will discuss treatment options including surgery, radiation, or chemotherapy.

FAQs about hard forearm lump

Will the lump in my forearm go away on its own?

Depending on the cause, there is a possibility that the lump and the accompanying pain will go away on its own. If the forearm lump is a cyst or caused by environmental or inflammatory conditions, there is a good chance it will resolve on its own. However, if the forearm lump is a benign or malignant tumor, it will not resolve on its own and will require specific treatment.

Will the lump spread from one forearm to the other?

If the lump is red or multiple lumps appear on one arm, this is most likely an inflammatory etiology like panniculitis. These bumps may spread and affect the other arm or another limb in the first few weeks; however, they can be easily treated and often resolve on their own. Other causes of forearm lumps, on the other hand, usually do not spread from one forearm to the other.

Is the lump chronic or temporary?

A forearm lump may be temporary or chronic depending on the cause. A chronic forearm lump is more associated with benign or malignant growths, whereas temporary lumps are more associated with traumatic or inflammatory causes. However, arthritic nodules are a chronic, inflammatory etiology and need proper follow-up with a specialist, such as a rheumatologist.

How will the lump affect my daily activities?

A forearm lump can be very painful and uncomfortable, but those related to temporary etiologies should not affect you long-term. After a traumatic event, bed rest and limited activity with the affected forearm will help with recovery. A forearm lump associated with a benign or malignant growth may cause fatigue or unexplained weight loss, which may inhibit your energy to complete tasks. See your physician promptly if you feel like your symptoms are significantly affecting your life.

What can I do to prevent the development of forearm lumps?

It is very difficult to prevent the development of forearm lumps. The only situations in which the development of forearm lumps may be prevented are those related to environmental factors. There are several strategies you can employ to prevent bites from occurring, such as wearing protective clothing, using insect repellent, and going outside at times when mosquitoes are less active (during the day, after dawn, and before dusk).

Questions your doctor may ask about hard forearm lump

  • What color is the bump?
  • Is your forearm bump painful to the touch?
  • Any fever today or during the last week?
  • Do you have a rash?

Self-diagnose with our free Buoy Assistant if you answer yes on any of these questions.

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The stories shared below are not written by Buoy employees. Buoy does not endorse any of the information in these stories. Whenever you have questions or concerns about a medical condition, you should always contact your doctor or a healthcare provider.
Dr. Rothschild has been a faculty member at Brigham and Women’s Hospital where he is an Associate Professor of Medicine at Harvard Medical School. He currently practices as a hospitalist at Newton Wellesley Hospital. In 1978, Dr. Rothschild received his MD at the Medical College of Wisconsin and trained in internal medicine followed by a fellowship in critical care medicine. He also received an MP...
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  1. Swenson R. Basic human anatomy. Dartmouth College. Published 2008. Dartmouth College Link
  2. Lumps. NHS. Updated December 18, 2017. NHS Link
  3. Lumps on forearm. The Journal of Family Practice. 2015;64(5). MDedge Link
  4. Signs and symptoms of soft tissue sarcomas. Updated April 6, 2018. American Cancer Society