Moles and melanoma on the nail, how to identify them?

Some time ago, I gave a talk at a congress to my dermatologist colleagues about moles and melanoma on the nails. I thought it would be important to share this information with my patients and blog readers. During the talk, I shared several clinical cases of patients who had spots on their nails that turned out to be melanomas. Seeing the interest and concern in the eyes of my colleagues, I realized the importance of spreading this knowledge and raising awareness about the importance of taking care of our nails. 

My name is Sebastian Podlipnik and I'm a skin cancer specialist at the Hospital Clinic de Barcelona. During my years of experience I have seen many cases of moles and melanoma on the nail and it is one of the reasons why I decided to write this blog. 

In this entry, We will learn how moles look on the nails, how to detect suspicious changes of skin cancer and when to consult a dermatologist.. In addition, I will share with you many pictures of nails so that we can identify them with good images. 

I accompany you on this journey of dermatological knowledge!

illustration of a longitudinal melanonychia that can occur in moles and melanoma of the nail

What will I talk about in this article?

What do moles and melanoma on the nail look like?

Moles are common on our skin and are usually harmless. However, when it comes to moles on the nails, it is important to pay special attention to them. 

Often, the following can be observed nail stains brown or black that adopt a linear shape, technically called ".longitudinal melanonychia". They are usually seen as brown or black lines that affect the length of the nail. 

Depending on their characteristics they may correspond to benign lesions or even in some cases to malignant lesions such as melanoma. In general terms Moles are small, well-defined lines, while the Melanomas are more chaotic, with larger spots and the pigment may extend beyond the nail. 



Illustration of a mole on the fingernail


Illustration of a melanoma on the fingernail

These small brown marks may seem insignificant, but in some cases they could be signs of melanoma, an aggressive form of skin cancer.  

Why do moles and melanoma look like brown or black lines?

This is because the cells that produce the pigment (melanocytes) are located in the nail matrix, which as you can see in the following image, is the most proximal area of the nail. If there is an increase of melanocytes (proliferation), either by a mole or a melanoma, the pigment will adhere to the nail plate (nail) and will advance as the nail grows. 

Illustration of a longitudinal melanonychia showing how they grow from the matrix to the nail plate.

What do moles look like on the nails?

Generally speaking, nail moles are very stable lesions and should not change significantly over time. They usually present with a band of pigment that affects only one nail. 

Clinical image showing a black line on the nail of a child. Also known as longitudinal melanonychia or nail mole.

Clinical photo of a mole on the nail. Image obtained from European Journal of Pediatric Dermatology

Dermatoscopic photo of a mole or nevus on the nail

Dermoscopic photo showing a regular pigmented band corresponding to a nail mole. 

What signs should lead one to suspect melanoma of the nail?

There are several signs that may lead us to suspect a malignant lesion of the nail and we will review them so that you have the diagnostic clues. Possibly one of the most important is that a malignant lesion usually only affects 1 nail. If, on the other hand, you notice the appearance of these spots simultaneously on several nails, possibly the cause of the pigmentation is something else that we will see later in the blog.  

That there be progressive changes

You will find that moles and benign nail lesions are very stable, so we do not expect them to grow or change over time. One of the first signs that we will see in melanoma of the nails are progressive changes such as those shown in the following image. 

Illustration showing the progression of a melanoma on the nail.

Triangular shape of the pigment line

Maybe this is a little bit more difficult to explain and understand, but if you remember what I explained previously that melanocytes are located in the nail matrix and then attach to the nail as it grows. 

Therefore, if we have a fast growing lesion it will rapidly increase in size in the proximal part of the nail, however the pigment found in the more distal part will be the pigment that "stuck" several months ago to the nail. 

Illustration showing the triangular shape of a melanonychia on the nail representing a melanoma.
photo of a melanonoma on the nail with triangular shape

Image obtained from Clinics in Dermatology

Other important signs

There are other important signs to be mentioned that are already present in more advanced lesions. These are:

  • Thickness more than ⅓ of the nail: If the band of pigment on the nail measures more than one third of the total width of the nail we should be concerned. 
  • Pigmentation beyond the nail: If we observe that the brown pigmentation extends to the skin adjacent to the nail.
  • Hutchinson's sign: If the pigmentation also affects the proximal nail fold. 
Signs of malignancy in nail melanoma

Now we are going to see a picture of a patient presenting some signs of malignancy in a nail affected by melanoma. If you have any of these signs, it is important to consult a dermatologist. 

Illustration showing the signs of malignancy of moles or melanoma of the nail.

Are there other causes of brown and black lines on the nails?

Before I continue, I would like to give you some peace of mind as the appearance of brown or black spots on the nail can have different causesThe most of them are not serious. We have already reviewed moles and melanoma which correspond to a growth of melanocytes (melanocytic proliferation). But, there are also other times when melanocytes can be activated and also produce brown or black lines on the nails. 

Classification of nail stains

Flowchart showing the causes of moles and melanoma of the nail

Generally speaking, we can classify nail stains as longitudinal melanonychia due to melanocyte activation or melanocyte proliferation.

The causes of melanocyte activation can be very broad, and most often several nails are affected at the same time, unlike moles or melanoma that usually affects only one. 

The most frequent causes of melanocytic activation are

  • Pregnancy
  • Trauma
  • Nail biting
  • Nail infection
  • Lichen planus
  • Psoriasis
  • Viral warts
  • Addison's disease
  • Hyperthyroidism
  • Photosensitivity
  • Lupus
  • HIV
  • Phototherapy
  • X-ray exposure
  • Antimalarial drugs
  • Chemotherapy drugs
Dermatological image showing melanonychia on multiple nails due to drugs.

Image obtained from bmj case reports

What do we do in the dermatological office when we see a melanonychia?

To properly evaluate a patient with a melanonychia, we perform a series of procedures to establish a diagnosis. 

1- physical examination

To begin with, I will conduct an examination complete physic of all your nails, both fingernails and toenails. This involves evaluating any deformities, the presence of melanonychia on multiple nails, as well as the color, shape and size of the affected areas. In addition, I will review your medical history to identify any underlying conditions that may be causing your nail staining.

2- Dermatoscopy (onychoscopy)

The next step in the diagnostic process involves a dermatoscopic examination. I will use a specific type of microscope to closely examine the suspicious areas. During this examination, my main focus will be to determine if there are signs that the melanonychia may be malignant.

3- Take a course of action with the injury

After completing the above two steps, we will assess whether the lesion is benign, suspicious or malignant. 

  • Benign lesion: If it is very clear to us that the reason for the pigmentation in the nail is benign, we can indicate a treatment to improve or discharge if it does not require further studies. 
  • Suspicious lesion, but not clearly malignant: Sometimes we will not have enough information to be able to establish a clinical diagnosis of the spot on the nail. In these cases it will be necessary to perform a digital follow-up of the nail or we may also request a biopsy. 
  • Lesion clearly suspicious of malignancy: In this case, we will directly assess the possibility of nail surgery to remove the lesion completely and biopsy it in its entirety. 

Conclusions on moles and melanoma of the nail

When it comes to evaluating nail stains, I recommend that you do it in person. This way, he will be able to examine your spot with dermoscopy and provide you with an accurate diagnosis.

Dermatoscopy Sebastian Podlipnik

Consultation with an expert

If you have a nail stain of this type that concerns you, it is important that you consult a specialist. 

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Sebastian Podlipnik - Skin cancer

Sebastian Podlipnik

Dermatology Blog

I am a dermatologist and cum laude MD and author of multiple research studies. I specialize in skin cancer, laser technologies and cosmetic dermatology. The intention of this blog is to bring you closer to topics of interest in dermatology and research.

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