Lumps and bumps along the hairline at the back of the neck may be due to skin irritation, acne, cysts, boils, muscle knots, and other causes.

The skin on the neck hairline frequently comes into contact with potential irritants, such as shampoo, clothing detergent, sweat, and hair-care products. This area of skin is also subject to friction from a person’s hair and clothes. Irritation and friction can sometimes lead to lumps, bumps, and other skin problems.

In this article, we describe some of the most common causes of lumps on the back of the neck or along the hairline. We also cover when to see a doctor.

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An infection can cause the lymph nodes to swell.

The lymph system is part of the immune system and comprises a network of lymph vessels and lymph nodes. Lymph nodes help the body kill germs and filter out harmful substances from the fluid that travels along the lymph vessels.

When lymph nodes swell, it can be a sign that the body is fighting an infection, such as a common cold or the flu.

Several lymph nodes run along the back of the neck, on either side of the spine. There are also lymph nodes behind each ear.

A lump on the back of the neck may be a swollen lymph node if it:

  • feels tender
  • is around the size of a marble
  • moves slightly when a person touches it

Sometimes lymph nodes swell when there is an infection nearby. For example, a swollen lymph node on the neck can be a sign of an ear or throat infection. The swelling tends to go down when the infection clears up.

Less commonly, swollen lymph nodes can indicate a noninfectious condition, such as rheumatoid arthritis or cancer.

Lymph nodes can also swell for no apparent reason.

It is advisable for anyone who has swollen lymph nodes to see a doctor if the swelling gets worse or does not disappear after a few weeks.

Acne can cause lumps and swellings at the back of the neck. Acne is a common skin condition that can occur when oil, bacteria, or dead skin cells block the pores or hair follicles.

Acne can develop on any part of the body where hairs grow, but common sites include the face, neck, and shoulders.

Acne outbreaks are common during puberty and adolescence due to hormonal changes. People of any age can get acne, however.

Types of acne lesion include:

Hair products, sweat, and clothing can irritate the back on the neck, all of which can make acne worse.

A person can often treat acne on the back of the neck at home with over-the-counter (OTC) remedies. Other tips include switching shampoos, keeping the neck clean and dry, and keeping the hair off the neck.

If acne is severe, very painful, or does not respond to home remedies, a dermatologist may prescribe a stronger medication.

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A cancerous mole may have an irregular border.

If the lump feels fleshy and is on top of the skin, rather than beneath the skin or in the muscle, it may be a mole.

Most people have some moles on their body. Moles typically appear during childhood, but new moles can develop at any age.

While most moles are harmless, they can sometimes become cancerous. So, it is essential to monitor moles, particularly new moles, for changes that can signal cancer.

A person can use the ABCDE rule to check for signs of skin cancer:

  • Asymmetry: One half of the mole is different in appearance to the other half.
  • Border: The mole has an uneven or irregular border or edge.
  • Color: The color is uneven, or there are unusual shades, such as blue and red.
  • Diameter: The mole is wider than 6 millimeters, which is around the size of a pencil eraser.
  • Evolving: The mole is changing in appearance over time.

People who suspect that a mole is cancerous should consult a primary care doctor or dermatologist. They can also consider scheduling an annual checkup with a dermatologist to ensure all their moles are healthy.

A sebaceous cyst is a fluid-filled lump that sits just below the surface of the skin. These cysts tend to be slow growing but can get very large.

Sebaceous cysts are generally harmless and are usually painless. Cysts can come and go, or they may continue to grow larger.

Some cysts come to a head or ooze when a person squeezes them. Popping a cyst, however, will not get rid of it, and it can cause an infection. Doctors can often remove a cyst with a simple, in-office procedure.

A person can see a doctor if the cyst becomes painful, tender, or red, as this is a sign of infection. Infected cysts may resemble large pimples.

Warm compresses and OTC pain medication can help relieve discomfort from an infected cyst.

A red, painful, pus-filled bump on the back of the neck may be a boil.

Boils, or furuncles, result from localized bacterial infections, which means that the infection is not affecting the surrounding skin or tissues. Cysts, acne, and blocked hair follicles can become infected and turn into boils.

Squeezing a boil can cause the infection to get worse or spread. Instead, applying warm compresses and keeping the area clean can ease the discomfort.

Again, it is advisable to see a doctor if the boil lasts more than a few days, is very painful, or a fever develops. A doctor may drain the boil or prescribe antibiotics.

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Skin irritation can cause lumps to appear.

Many substances can irritate the back of the neck. Shampoo, hair products, clothing detergent, sweat, and sunscreen can cause skin irritation or allergic reactions in some people. Friction from clothing can sometimes also irritate the neck, causing a rash.

If the lump is small, red, and itchy, or there are patches of dry skin on the neck, it may be a sign of skin irritation or an allergic reaction.

To reduce or prevent skin reactions try:

  • changing or using less skin and hair products
  • trying a different detergent for clothes washing
  • keeping the hair off the neck
  • keeping the neck clean and dry

Moisturizers and OTC antihistamine creams and tablets may also help to relieve symptoms. Seeing a doctor is an option if skin reactions or rashes are severe or persistent.

Injured or tense muscles can form knots, or myofascial trigger points, that a person can feel just below the skin. These tense bands of muscle tissue can vary considerably in size but do not usually cause a visible lump or bump above the surface.

The neck is a typical site for muscle pain and tension. Long days sat working at a computer or desk can strain the muscles and irritate the nerves around the hairline.

Muscle knots can be painful, sore, or tense, but they are not usually a serious health problem. However, they can affect a person’s mobility and sleep and can sometimes lead to other issues, such as headaches.

Ways to help relieve or prevent muscles knots in the neck include:

  • massage
  • gentle stretching
  • frequent breaks from computers and desk
  • maintaining a good posture while sitting
  • making adjustments to workstations

Lumps or bumps near the hairline at the back of the neck are usually not a cause for concern. Possible causes of lumps in this area can include acne, muscle knots, boils, and skin irritation.

Speak to a doctor for lumps that are painful, do not go away after a few days, or accompany other concerning symptoms. Also see a doctor for new or existing moles that change in color, shape, or size.