Birthmark 'mole'

A mole commonly referred to as a "mouse" is a benign pigmented skin lesion, usually dark in color (brown or black), small in size, and regular in shape. This term is not a medical name but a descriptive term used by patients – it usually refers to a small melanocytic nevus resembling the shape of a mouse's head (e.g., with "ears") or a distinctly defined, round mole. In most cases, it is a **pigmented nevus (nevus melanocyticus)**, which is a cluster of melanocytes – cells that produce melanin. Although these lesions are typically benign, any new or changing skin lesion requires dermatological evaluation.

Mole nevus - cause

The formation of melanocytic nevi is a multifactorial process and depends on:

1. Genetic factors

Family predisposition to the occurrence of numerous nevi.
Somatic mutations within melanocytes (e.g., in BRAF, NRAS genes) leading to their local proliferation.
Congenital disturbances in melanocyte migration during the embryonic period (in the case of congenital nevi).

2. Exposure to UV radiation

Ultraviolet radiation (UVB and UVA) stimulates melanocyte proliferation.
Intense sunburns in childhood increase the number of acquired nevi.
Excessive sun exposure promotes the development of new pigmented lesions.

3. Hormonal changes

Puberty, pregnancy, or hormone therapies can increase melanocyte activity.
Lesions may undergo temporary darkening under the influence of hormones.

In clinical practice, a "mole" most commonly refers to a small acquired pigmented nevus that appears in childhood or adolescence.

Birthmark mole – what it means

In the vast majority of cases, a mole referred to as a "mouse":

is of a benign nature,
is well-defined,
has a uniform color,
grows proportionally with body growth (in the case of congenital changes).

It is not a disease entity in itself. However, the clinical significance of a mole depends on its morphological features. The ABCDE rule is used in diagnostics, which helps assess the risk of cancerous transformation:

A (Asymmetry) – asymmetry,
B (Border) – irregular borders,
C (Color) – uneven color,
D (Diameter) – diameter over 6 mm,
E (Evolution) – change over time (shape, color, size).

If the "mouse":

begins to grow rapidly,
changes color,
bleeds or itches,
has irregular borders,

it requires urgent dermatological consultation and dermatoscopic examination.

It is worth emphasizing that the mere presence of a mole does not indicate an increased risk of melanoma, provided it does not exhibit atypical features.

Birthmark mouse from birth

A birthmark present since birth most commonly corresponds to a congenital melanocytic nevus (nevus melanocyticus congenitus). It forms during the fetal stage due to disturbed migration or proliferation of melanoblasts (precursors of melanocytes).

Congenital nevi are classified by size:

Small – up to 1.5 cm,
Medium – 1.5–20 cm,
Large / Giant – over 20 cm.

Small congenital nevi (the typical "mole" from birth):

have a very low risk of malignant transformation,
usually do not require prophylactic removal,
should be clinically and dermoscopically monitored.

The risk of melanoma significantly increases only in the case of large and giant congenital nevi.

Features of a congenital nevus:

presence from the time of birth,
proportional growth with the child,
often presence of hair within the lesion,
uniform or slightly heterogeneous pigmentation.

The decision to potentially remove a small congenital nevus is made individually – usually for aesthetic reasons or in the case of concerning morphological changes.

Diagnostyka i postępowanie

Podstawą oceny jest:

badanie dermatologiczne,
dermatoskopia (nieinwazyjna ocena struktur barwnikowych),
w uzasadnionych przypadkach – wycięcie chirurgiczne z badaniem histopatologicznym.

Nie zaleca się:

usuwania znamion metodami niesprawdzonymi,
wypalania czy krioterapii bez uprzedniej diagnostyki histopatologicznej,
samodzielnego drażnienia zmiany.

Profilaktyka obejmuje:

ochronę przeciwsłoneczną SPF 30–50,
unikanie solarium,
regularne samobadanie skóry,
kontrolę dermatologiczną raz w roku u osób z licznymi znamionami.