A cutaneous horn is a growth on the skin, and developing any new growth can be a cause for concern.

Cutaneous horns are lesions that develop on the skin from an overgrowth of keratin. This is the protein responsible for making hair, nails, hoofs, and horns. An overgrowth of this protein is called hyperkeratosis.

The lesions usually develop in areas frequently exposed to the sun. About 60% of all cutaneous horns are benign, while others are cancerous or precancerous. Because of this, anyone who develops a cutaneous horn should seek medical attention.

Below, we explore the causes and risk factors for cutaneous horns, as well as how to identify one and when to contact a healthcare professional.

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Cutaneous horns are growths that resemble an animal’s horn. They are hard and brownish yellow.

The difference between a cutaneous horn and the horn on an animal is that the latter forms around a central bone, while cutaneous horns do not.

These growths most commonly develop on the face, ears, and the back of the hand. They can also form on the nails, especially that of the big toe. Rarely, a horn may form on the penis.

Cutaneous horns develop from an excessive growth of keratin on the skin, particularly in very sun-damaged areas. The growths may be harmless, precancerous, or cancerous. There may be an underlying cyst, though this is extremely rare.

Because cutaneous horns tend to develop in areas often exposed to the sun, particularly on the face and hands, experts believe that they may be related to high levels of UV radiation.

Research indicates that, while anyone can develop a cutaneous horn, people with a greater risk include:

  • people with fair skin
  • people with a human papillomavirus, or HPV, infection
  • older adults
  • people with high levels of sun-damaged skin

In addition, males are more likely than females to develop these growths — and they are more likely to develop malignant ones.

In terms of cancer risk, cutaneous horns on the face are more likely to be cancerous or precancerous than those elsewhere on the body. And the risk of malignancy increases with the size of the horn.

Cutaneous horns on dogs and cats

Animals other than humans can develop these growths, including malignant ones.

In cats, especially, cutaneous horns are quite common and usually form on the footpads. The cause is typically feline leukemia virus-associated dermatoses or a feline papillomavirus infection.

Less often, cutaneous horns form in dogs as a result of a canine papillomavirus infection.

A doctor can often diagnose a cutaneous horn based on its appearance alone:

  • The horn-like growth on the skin’s surface is typically brownish yellow and curved.
  • The growths usually appear on the face, hands, forearms, or ears.
  • The surrounding skin may be unchanged or slightly thickened.
  • The growth is usually a few millimeters or centimeters long, or twice as long as the base is wide.
  • Rarely, cutaneous horns can grow much larger.
  • Rarely, more than one of these growths develop, in a group.

Most cutaneous horns cause no other symptoms. However, when a horn is damaged, there may be pain or an infection.

Anyone who may have a cutaneous horn should schedule an appointment with a healthcare professional to have it evaluated for skin cancer.

People who already have a cutaneous horn diagnosis should contact a doctor if any of the following symptoms develop:

  • pain
  • an increase in the size of the horn
  • redness at the base of the horn
  • the horn becoming wider than it is tall
  • hardening or puckering of the surrounding skin

The changes above can indicate that the horn may have become cancerous.

Doctors associate a range of health issues with cutaneous horns.

Many of these health conditions are noncancerous, including nevi, seborrheic keratoses, viral warts, viral skin infections, and psoriasis. The latter two require medical treatment, while the others are benign.

Another growth, called a keratoacanthoma can develop from a cutaneous horn, though this is rare. This type of growth is relatively common and often benign. It is dome-shaped and can grow up to 3 centimeters in diameter. Older people, people with lighter skin, and those with sun damage have a higher risk.

A doctor may recommend surgical removal to reduce the risk of a keratoacanthoma becoming malignant, as it can resemble squamous cell carcinoma, a type of cancer.

Below, we describe the more serious conditions related to cutaneous horns that are either cancerous or precancerous.

Cutaneous horn squamous cell carcinoma

Squamous cell carcinoma is the most common skin cancer that can occur with a cutaneous horn. It develops in about 94% of all malignant cutaneous horn cases.

There may be a greater risk of developing squamous cell carcinoma, in particular, if the cutaneous horn is larger and painful, or red and wider at its base.

If the horn is located on an ear, the back of a hand, the scalp, the nose, a forearm, the penis, or the face, it may also be linked with squamous cell carcinoma.

A cutaneous horn can also present as an early version of this cancer, known as Bowen’s disease or squamous cell carcinoma in situ.

Cutaneous horn basal cell carcinoma

A more rare type of cancer associated with a cutaneous horn is basal cell carcinoma.

Risk factors include excessive exposure to the sun or ionizing radiation, which can come from X-ray or CAT scan machines.

Age, genetics, having a weakened immune system, and having scarring, may also increase the risk.

Cutaneous horn melanoma

Melanoma developing from a cutaneous horn is very rare, and the exact link remains unclear.

Contributing factors may include sun exposure, an ongoing inflammatory process in the skin, and an overgrowth of blood vessels.

Understanding how a cutaneous horn develops into this type of skin cancer requires further research.

To determine whether a cutaneous horn is malignant, a doctor usually orders a biopsy. This involves taking a sample of the horn that includes a piece of the base.

Cutaneous horn removal

In some cases, a doctor recommends removing the entire horn. This is especially important when malignancy is a significant concern.

In the process, the doctor takes a biopsy to check for any indications of cancer. It is rare for a doctor to be able to rule out malignancy without a biopsy. For this reason, a doctor will almost always request a biopsy for the horn.

A biopsy involves taking a sample of the growth and analyzing it for signs of malignancy in a laboratory. Depending on the results, additional treatment may be necessary.

When a biopsy confirms that the growth is benign, the person may choose to leave the lesion or remove it for aesthetic reasons.

Never try to remove a cutaneous horn at home. A healthcare professional needs to remove it in a clinical setting.

Additional treatment options

It is important for a doctor to determine whether a cutaneous horn is benign or potentially harmful with a biopsy before any destruction of the horn.

Anyone who then wants to have a benign growth destroyed for cosmetic reasons might consider laser therapy or electrocautery, which involves a healthcare professional using heat to destroy the horn’s tissue.

However, having the horn removed by a doctor is still the most common choice.

Once a doctor removes a cutaneous horn, the outlook is usually good, even when the growth was cancerous. Most people do not need further treatment after the removal.

However, if basal cell or squamous cell cancer was the horn’s underlying cause, a person needs to have regular screening to determine whether the cancer has returned.

Cutaneous horns are hard, brownish-yellow growths on the skin. They develop due to an excessive production of keratin, a protein that also forms the hair and nails. Cutaneous horns may be benign, precancerous, or cancerous.

About 40% of all cutaneous horns are malignant, and the most common associated skin cancer is squamous cell carcinoma.

For this reason, anyone who may have a cuteanous horns should contact a doctor for a biopsy to determine whether the growth is cancerous.

After the doctor removes the growth, most people do not need further treatment, though they may need regular screening to determine whether the cancer has returned.