Hard, Painful, Pea Sized Lump Under Skin on Forearm: Causes, Symptoms and When to Worry

A lump under the skin on the forearm can be caused by an infection, tumor or injury. In most cases, such a lump will not be serious enough to call for medical treatment. Diagnosis is however very important for confirmation.

Lumps that occur under the skin are usually not very painful. Some can involve the forearm bone and as a result cause much pain. Conditions such as arthritis will not only cause lumps at the elbow joint but will also reduce forearm functionality. In this article, we will discuss the common causes of lumps on the forearm under skin and forearm bone. Remember that your doctor will be best suited to direct if the lump should be treated or left alone.

Painful lump on forearm muscle after injury

Injuries are common causes of lumps on forearm muscle. The lump can be caused by:

  • Hematoma – a hematoma is a lump that forms when blood collects under skin after damage to blood vessels. A hematoma lump inside cheek can develop after a simple injury such as biting your cheek. In most cases, hematomas are red or bluish in color. They don’t require medical treatment and do resolve within 2-4 weeks. You can try warm compressing on the lump about 24 hours after its formation.
  • Forearm bone bruise – a hard lump under bruise on forearm bone can develop if the bone is injured such as after a direct blow with a blunt object. Like hematomas, bone bruises resolve even without treatment. Diagnosis may be required to rule out fractured forearm bone.
  • Muscle injuries – Muscles or ligaments in forearm can strain or tear. Muscle strains are fairly mild and heal without treatment. Torn muscles require some medical attention and tend to form larger lumps.

A painful lump on the forearm muscle after injury should be treated by a doctor if it develops 30 minutes or less after the injury. Also, see your doctor if you experience symptoms such as intolerable pain, swelling, and inability to use your arm.

Soft or hard lump on forearm that grows in size

A soft or hard lump on forearm that keeps growing in size should cause you concern. Gradual gaining of mass is usually associated with cancerous lumps. All the same, rarely will a lump on your forearm indicate cancer. Types of forearm tumors include:


This is one of the most common causes of tumors under the skin. A lipoma is a noncancerous slow-growth that originates in fatty tissues. You can have multiple lipomas around the same area or distributed throughout the body. A small lipoma can start as a pea-sized lump in forearm but enlarge to reach 2 cm in diameter. Giant lipomas can reach 5 cm in diameter but rarely occur in upper extremities. Lipomas form soft, rubbery and movable lumps under the skin.


A fibroma is a noncancerous growth that originates in connective tissues. It is not clear what causes fibromas but they tend to develop after trauma or irritation. Generally, fibromas are not painful. Pain can, however, develop if the lump pushes against a nerve. Most fibromas form noticeable, firm lumps under the skin. The lump can keep growing or remain the same size.


Cysts are sac-like lumps that form under skin. Sebaceous cysts are most likely to develop on your forearm. Generally, cysts are not painful and feel slightly movable. A cyst can keep enlarging or remain in the same position for a long time. For example a lump in the lower left abdomen caused by an ovarian cyst can get so big that it displaces the ovaries. Cysts don’t disappear unless removed.


Moles are very common benign growths that appear on the skin. They can be red or brown in color. Normally, moles develop by the time you are 20 years and do not increase in size.


Warts are skin growths caused by HPV. Most of them form fleshy growths that take the color of skin and may resemble a cauliflower. They are not dangerous but often require treatment. The forearm is not the most common part of the body you will find warts. The genital area is the most common place where warts develop. You can learn more on how to remove wart lump on my labia or genitals here.


Skin cancer is the most likely to form a hard lump on forearm. It can be melanoma or non-melanoma. Melanoma cancer cells originate in melanocytes or the cells that give the skin its pigment. In most cases, it is characterized by the formation of an evolving mole-like lump or spot on the skin. Non-melanoma skin cancer originates in skin cells below the superficial layer. Lymphoma or cancer of the lymphatic system can also be responsible. See your doctor if you notice a lump on your forearm that persists for more than 2 weeks, has no identifiable cause or causes masses elsewhere in the body such as a white lump on gums.

Hard lump on forearm near elbow

Some conditions that can cause a hard lump on forearm near the elbow include:


This is a degenerative disease of the joints that causes wear and tear of bone cartilages. Swelling and pain may occur around the affected joint. As bones in the elbow joint grate against each other, a bone spur will form. This is a hard, bony growth that originates in bones.

Rheumatoid arthritis

This is an autoimmune disease of the joints. It develops when the immune system attacks healthy joints. The disease is characterized by formation of hard nodules around the affected joint. The nodules are usually painful.


Gout is closely related to arthritis. It affects joints and causes small lumps or nodules due to accumulation of uric acid. Affected joints also swell and become tender and very painful.

Elbow joint injuries

Injuries can occur on muscles, ligaments, tissues or bones that form the elbow joint. If swelling, tenderness and pain occur, see your doctor for X-ray imaging.

Small, soft lump on forearm skin

A small soft lump on forearm skin can be a boil or an abscess. Boils originate in clogged hair follicles and sometimes in oil glands. A staphylococcus bacteria strain that thrives on the skin finds a way into the clogged follicles. Naturally, the immune system will attack the clogged dirt and bacteria. This results in dead cells, pus and other forms of dirt.

Boils mature in about 5 days. Then, the white tip which is usually above the skin ruptures. Some boils don’t rupture but crust over at the height of their maturity.

Large boils form abscesses. These are more serious infections which can spread or cause other symptoms such as fever, swollen lymph nodes and fatigue.

Other than boils, a soft lump on forearm skin can be caused by folliculitis. This is inflammation of hair follicles. It causes red, painful bumps around a hair follicle. Severe folliculitis can result in a cluster of boils known as a carbuncle.

When to see a doctor

There are other possible causes of forearm lumps not covered in this article. Such include infections such as cellulitis and tumors such as neurofibromas. It is for such reasons that medical diagnosis is very important.


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