Lentigines are common pigmented spots on the skin that are harmless. These spots are frequently referred to as “age spots” or “liver spots,” though they have no connection to the liver’s function or health. Lentigines appear when there is an increase in the number of pigment-producing cells in a localized area of the skin. They are highly prevalent, especially as people age, and represent one of the most common signs of cumulative sun damage. Understanding these spots involves recognizing their physical characteristics, biological origins, and the differences between their various types.
Physical Appearance and Location
Lentigines present as flat or slightly raised patches of skin discoloration, ranging from light tan to dark brown or black. They possess clearly defined, sharp borders and are typically round or oval in shape. Most benign lentigines are small, usually measuring a few millimeters in diameter, though they can slowly grow up to two centimeters.
These pigmented macules are most commonly found on areas of the body that receive chronic sun exposure over a lifetime. Typical locations include the face, neck, shoulders, upper back, and the backs of the hands and forearms. Unlike freckles, lentigines do not fade or disappear during the winter months. This persistence is a key characteristic that differentiates them from the temporary darkening observed in freckles.
Underlying Causes and Development
The formation of a lentigo is a biological response within the skin’s epidermis, driven primarily by exposure to ultraviolet (UV) radiation. This chronic exposure triggers the over-proliferation of melanocytes, the cells responsible for producing the pigment melanin. In a lentigo, there is an increased density of these melanocytes concentrated within the basal layer of the epidermis, the skin’s outermost layer.
Histological analysis shows that the skin architecture in a lentigo typically includes a lengthening of the rete ridges, which are the downward projections of the epidermis. This lengthening provides more surface area for the increased number of melanocytes to reside, leading to the localized hyperpigmentation. Genetic predisposition also contributes, as individuals with lighter skin types are more susceptible to this melanocyte proliferation due to reduced ability to block UV penetration.
Classification of Lentigines
Lentigines are classified into two main benign categories based on their cause, but a third, potentially serious form requires distinction.
Solar Lentigines
Solar Lentigines, also known as sun spots, are the most common type and are directly linked to cumulative UV exposure. These usually begin to appear in middle age on sun-exposed skin, often signifying a history of photodamage.
Simple Lentigines
Simple Lentigines (lentigo simplex) are not associated with sun exposure or systemic disease. They often appear at birth or during childhood on any body site, including areas protected from the sun. They are generally smaller and fewer in number compared to the solar type, and their presence is typically linked to genetic factors.
Lentigo Maligna
The most important distinction is Lentigo Maligna (LM), which is a form of melanoma in situ, meaning the cancerous cells are confined to the top layer of the skin. LM frequently develops on chronically sun-damaged skin, most often on the face and neck of older individuals. Unlike the uniform color and regular border of a benign lentigo, Lentigo Maligna exhibits atypical features, which are evaluated using the “ABCDE” rule.
The ABCDE rule helps differentiate concerning lesions:
- Asymmetry (one half does not match the other).
- Border irregularity (notched or poorly defined edges).
- Color variation (multiple shades of brown, black, white, or pink within the same lesion).
- Diameter greater than 6 millimeters.
- Evolving (a change in size, shape, or color over time).
Because early Lentigo Maligna can closely mimic a benign solar lentigo, any pigmented spot that is large, growing, or shows variegation in color must be examined by a specialist. A skin biopsy is the definitive diagnostic procedure to determine if the melanocytes have become malignant.
Treatment and Preventative Measures
Treatment for benign lentigines is generally sought for cosmetic reasons, as the spots themselves pose no health risk.
Topical Treatments
Topical treatments work by interfering with the pigment production process or increasing skin cell turnover. For instance, topical retinoids like tretinoin accelerate the shedding of pigmented cells. Hydroquinone works by inhibiting the enzyme necessary for melanin synthesis.
Procedural Options
Procedural options are often more effective for removal, particularly for solar lentigines. Cryotherapy involves the controlled application of liquid nitrogen to freeze and destroy the hyperpigmented melanocytes, which are more susceptible to cold temperatures. Pigment-specific laser treatments selectively target the melanin pigment with high-intensity light pulses, causing the pigment to shatter so the body can naturally clear it away.
Prevention
Preventative measures are the most effective way to manage lentigines and reduce the risk of developing Lentigo Maligna. This involves strict sun protection, including applying a broad-spectrum sunscreen with a Sun Protection Factor (SPF) of 30 or higher every day. Seeking shade during peak sun hours and wearing sun-protective clothing, such as wide-brimmed hats, also minimizes the UV exposure that drives melanocyte proliferation. It is important to schedule annual skin checks with a dermatologist and to monitor existing spots for any changes that align with the ABCDE characteristics.