Keratin Bump on a Cat: What Those Lumps Mean

Name: Keratin Bump on a Cat: What Those Lumps Mean
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-10-03

A keratin bump on a cat is a small, hard growth made mostly of keratin, the same protein that forms hair and claws. Most of these bumps are benign, but some skin tumors and infections can look almost identical, so a veterinarian should examine any new lump. This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

A keratin bump or cutaneous horn is a hardened, often cone-shaped growth on the skin surface. Many are harmless, but they can resemble more serious tumors.
Skin tumors are the most commonly seen tumors in cats, partly because they are easy to spot and because skin is constantly exposed to the environment [1].
Basal cell tumors are common in older cats and often appear as firm, hairless, or ulcerated lumps that may stick out like stalks [1].
Any lump that grows quickly, bleeds, ulcerates, or changes should be checked by a veterinarian.
Do not try to cut, pick, or freeze a lump at home. Let your veterinarian diagnose it.

What a Keratin Bump Looks Like and What Is Normal

A keratin bump on a cat often looks like a small, hard, raised area on the skin. Some are smooth and round. Others form a cone or spike shape, which is why they are sometimes called cutaneous horns. The surface may be dry, crusty, or slightly scaly. Color varies from pale to dark, depending on the cat and the cause.

The skin is the largest organ of your cat's body, and it constantly renews itself [2]. New skin cells form near the base of the epidermis and move upward in a process called keratinization. This creates a compact layer of dead cells on the surface [2]. When that process goes wrong in one spot, keratin can build up into a bump or horn.

Normal skin should be soft, flexible, and covered by fur. A small lump that stays the same size for months is often less concerning than one that changes. Still, you cannot tell a benign bump from a serious one just by looking at it. Only a veterinarian can do that.

If you are unsure whether a lump is worth a visit, this guide on Cat Skin Bumps and Lumps: When to See a Vet and When to Monitor can help you decide.

Main Causes of Keratin Bumps and Horns on Cats

Several conditions can cause a hard, keratinized lump on a cat. Some are harmless. Others need treatment.

Benign Growths

Basal cell tumors are one of the most common skin tumors in older cats [1]. They usually appear as firm, solitary lumps that may be hairless or ulcerated. Some stick out from the skin like stalks [1]. They can range from less than 0.4 inches (1 centimeter) to more than 4 inches (10 centimeters) across [1]. In cats, these tumors are often dark in color, and cysts may form inside them [1]. Basal cell tumors are benign, but some grow quickly and cause ulceration and inflammation [1]. Surgical removal works well [1].

Sebaceous gland problems can also cause crusty, dark skin lesions. One study described a cat with sebaceous gland dysplasia that had hair loss and dark crusts, with enlarged and abnormal sebaceous glands on biopsy [3]. This is a rare condition, but it shows that gland problems can mimic other lumps.

Some breeds have their own skin issues. Lykoi cats can develop a comedonal syndrome with papules and comedones, and biopsies showed infundibular follicular cysts in affected cats [4]. This is specific to that breed, but it is a reminder that genetics can play a role in skin bumps.

Cutaneous Horns

A cutaneous horn is a hard, cone-shaped growth made of keratin. It can form over a benign bump, but it can also form over a skin cancer. One report described a cat with a cutaneous horn and squamous cell carcinoma in situ (Bowen's disease) at the same time [5]. The cat had multiple crusted lesions and a horn on the lower back [5]. This case shows that a horn is not always harmless.

Infections and Other Causes

Not every lump is a tumor. Infections can create swelling, crusts, and draining wounds that look like growths. One report described a cat with chronic, non-healing draining wounds that turned out to be a mycobacterial infection, not cancer [6]. The cat had a mass that was initially thought to be a spindle cell tumor, but biopsy showed severe inflammation and no neoplasia [6]. The cat recovered after 24 weeks of treatment [6].

Sarcoma is a serious concern with any recurrent or deep mass. One report described a cat with a recurrent sarcoma near the hip that later invaded the spinal cord [7]. This is uncommon, but it shows why deep or recurring lumps need prompt attention.

Cause	Typical clues	How urgent
Basal cell tumor	Firm, hairless, dark lump, may be ulcerated or stalk-like, common in older cats [1]	Routine visit, but sooner if growing
Cutaneous horn	Hard, cone-shaped keratin growth, may sit over another lesion [5]	Routine visit, sooner if changing
Sebaceous gland dysplasia	Hair loss, dark crusts, abnormal glands on biopsy [3]	Routine visit
Lykoi comedonal syndrome	Papules and comedones, breed-specific [4]	Routine visit
Mycobacterial infection	Chronic draining wounds, swelling, poor response to antibiotics [6]	Prompt visit
Sarcoma	Deep, recurrent, or fast-growing mass [7]	Same day or emergency

Red Flags That Make It an Emergency

Most skin lumps are not emergencies. Some signs mean you should act right away.

The lump bleeds heavily and will not stop.
Your cat has trouble breathing, collapses, or seems weak.
The lump is near the eye, nose, mouth, or rectum and is affecting eating, breathing, or elimination.
The lump grows visibly in days, not months.
Your cat has a fever, stops eating, or becomes lethargic.
The lump ruptures and drains pus or foul fluid.

A sarcoma that invades deeper structures can cause nerve problems. One cat with a recurrent sarcoma developed progressive weakness in the back legs, fecal incontinence, and urinary retention when the tumor reached the spinal cord [7]. Those signs are emergencies.

If your cat has a skin rash with many small bumps instead of one lump, see Cat Skin Rash with Bumps: Common Causes and Next Steps.

Safe Things You Can Do at Home While Waiting

You cannot diagnose a lump at home. You can keep your cat comfortable and avoid making things worse.

Do not squeeze, pick, cut, or freeze the lump.
Do not apply human creams, oils, or essential oils. Cats lick their skin and can become sick.
Take a photo with a ruler or coin next to the lump so you can track size changes.
Write down when you first noticed it and whether it has changed.
Keep your cat indoors and away from rough surfaces that could irritate the lump.
Use a soft brush or your hands to check the rest of the body for other lumps.
If the lump is bleeding, apply gentle pressure with a clean cloth and call your veterinarian.

If your cat is licking or scratching the area, a cone or soft collar can help prevent trauma. Ask your veterinarian before using any product on the skin.

What the Veterinarian Will Check and Test

Your veterinarian will start with a full physical exam. They will feel the lump, measure it, and check the surrounding skin and lymph nodes. They will also look for other lumps elsewhere on the body.

Common next steps include:

Fine needle aspiration. A small needle collects cells from the lump. The cells are examined under a microscope. This can often tell the difference between a cyst, an infection, and a tumor.
Biopsy. A tissue sample gives a definitive diagnosis. This is often needed for hard or keratinized lumps because they do not release many cells.
Imaging. X-rays or ultrasound may be used if the lump is deep or if the veterinarian suspects it has spread.
Blood work. This checks your cat's general health before any surgery or treatment.

Basal cell tumors are usually removed surgically, and removal is effective [1]. If the lump is a cutaneous horn, the veterinarian will want to check the tissue underneath it, because a horn can form over a skin cancer [5]. If an infection is suspected, special cultures may be needed, as in the mycobacterial case where standard tests did not identify the organism until further testing was done [6].

Costs vary by clinic and by how many tests are needed. For a general idea of what to expect, see Cat Skin Bumps and Lumps: What the Vet Will Do and How Much It Costs.

Prevention and Monitoring

You cannot prevent every skin lump. You can lower some risks and catch problems early.

Check your cat's skin once a month. Run your hands over the body, including the back, legs, belly, and tail base.
Keep your cat indoors. This reduces sun exposure and fights that can cause wounds and infections.
Use sun protection for light-colored cats with thin fur on the ears and nose. Ask your veterinarian which product is safe.
Keep up with flea and tick control as recommended by your veterinarian.
Watch existing lumps for changes in size, color, or texture.
Schedule routine exams, especially for older cats. Basal cell tumors are common in older cats [1].

Some breeds may have a higher risk of certain skin tumors. Domestic longhair, Himalayan, and Persian cats are among the breeds most at risk for basal cell tumors [1]. If you have one of these breeds, regular skin checks are especially useful.

If your cat has hair loss on the back near the tail along with a lump, that pattern can have several causes. See Cat Hair Loss on Back Near Tail: What It Means.

Limitations and When to Contact a Veterinarian

No article can tell you what a specific lump is. Your veterinarian needs to see and test it. Individual cases need a veterinarian.

Contact your veterinarian the same day if:

The lump appeared suddenly and is growing fast.
The lump is bleeding, oozing, or has an open sore.
Your cat is licking, biting, or scratching at it constantly.
Your cat seems painful when the area is touched.
You notice new lumps elsewhere on the body.

Go to an emergency clinic now if:

Your cat is having trouble breathing or is collapsing.
There is heavy bleeding that will not stop.
Your cat cannot urinate or pass stool.
Your cat has sudden weakness in the back legs or cannot walk.

Schedule a routine visit if:

The lump is small, stable, and not bothering your cat.
You first noticed it weeks ago and it has not changed.
You want a baseline check and advice on monitoring.

When in doubt, call your veterinarian. A quick exam is safer than waiting.

Frequently Asked Questions

Is a keratin bump on a cat dangerous?

Most keratin bumps are benign, but some can be skin cancers or form over a cancer. A cutaneous horn was reported in a cat that also had squamous cell carcinoma in situ [5]. Because you cannot tell by looking, a veterinarian should examine any new or changing lump.

Can I remove a cutaneous horn at home?

No. Cutting or pulling a horn can cause bleeding, pain, and infection. It also removes tissue that your veterinarian needs to examine. The base of the horn must be checked for cancer, so removal should be done by a veterinarian.

Do keratin bumps on cats go away on their own?

Some cysts and minor bumps may shrink or stay the same for years. Others grow or become inflamed. There is no reliable way to predict which will go away. If a bump is growing, bleeding, or changing, have it checked.

Are certain cats more likely to get skin lumps?

Yes. Older cats are more likely to develop basal cell tumors, and domestic longhair, Himalayan, and Persian cats are among the breeds most at risk [1]. Lykoi cats can develop a breed-specific comedonal syndrome with papules and cysts [4]. Genetics and age both play a role.

What happens if the lump is cancer?

If the lump is cancer, treatment depends on the type and how early it is found. Basal cell tumors are benign and are usually cured with surgery [1]. Other cancers may need surgery, radiation, or other treatments. One cat with a recurrent sarcoma received surgery and radiation, though the tumor later spread [7]. Early diagnosis gives your cat the best options.

References

Tumors of the Skin in Cats - Cat Owners. Merck Veterinary Manual.
Structure of the Skin in Cats - Cat Owners. Merck Veterinary Manual.
SOAT1 Nonsense Variant in a Cat With Sebaceous Gland Dysplasia. Animal genetics, 2026.
Clinical, histopathological and genetic features of a cutaneous adnexal polycystic syndrome in Lykoi cats: a prospective study of 10 cases. Journal of feline medicine and surgery, 2026.
Cutaneous horn and squamous cell carcinoma in situ (Bowen's disease) in a cat. Journal of the American Animal Hospital Association, 1998.
Feline Cutaneous Mycobacteriosis Caused by Mycobacterium farcinogenes: The First Case Report from Asia. Animals : an open access journal from MDPI, 2026.
Suspected recurrent sarcoma resembling feline injection-site sarcoma with spinal cord invasion in a cat. JFMS open reports, 2026.