A birthmark is defined as a discoloration or formation on the skin that is present at birth or appears shortly thereafter. While the term suggests immediate visibility, many marks considered birthmarks may not become visible until days or even months after a baby is born. This delayed appearance is a normal part of the development for specific types of these common skin features. Understanding the different stages of these marks, from initial appearance to lifelong changes, offers a complete picture of their nature.
Congenital Marks: Present from Birth
Marks that are fully formed and visible the moment a baby is born represent the classic definition of a birthmark. These marks are classified into two main types based on their cellular origin: pigmented and vascular. Pigmented marks result from an overgrowth of color-producing cells and include congenital nevi (moles present at birth) and flat blue-gray patches known as Mongolian spots. Vascular marks arise from improperly formed blood vessels; an example is the port-wine stain, a flat patch of skin that ranges from pink to deep purple.
Why Some Birthmarks Appear Weeks or Months Later
The delayed manifestation of some birthmarks occurs because their cellular components take time to proliferate and become noticeable on the skin’s surface. The most common example of this delayed appearance is the infantile hemangioma, often called a “strawberry mark.” A baby might be born with no mark, or just a faint pale patch, only for the hemangioma to fully develop into a raised, bright-red lump days or weeks later. This delay occurs because the mark involves the rapid proliferation of blood vessel cells.
The growth phase for hemangiomas is rapid during the first few months of life, peaking around six months before stabilizing. Some pigmented spots, such as café-au-lait spots, may also emerge during early childhood rather than being present at birth. These spots, which are the color of coffee with milk, become visible as pigment-producing cells cluster and produce more melanin. The delayed visibility is a normal part of their developmental timeline.
How Existing Birthmarks Change Throughout Life
Once a birthmark has appeared, it commonly changes significantly over time, a process distinct from its initial development. Many infantile hemangiomas undergo a natural process called involution, meaning they shrink and fade over a period of years. The majority of these vascular marks resolve completely by the time a child reaches five to ten years old. Pigmented birthmarks, such as congenital nevi, will grow proportionally as the child’s body grows.
Other changes can be influenced by internal and external factors throughout a person’s life. Hormonal changes, particularly during puberty or pregnancy, can cause existing moles to darken or increase in size. Exposure to sunlight can also influence the appearance of pigmented marks by increasing melanin production. Port-wine stains, which do not involute, tend to darken and may become thicker or develop a slightly lumpy surface in middle adulthood.
Distinguishing New Marks from True Birthmarks
If a new spot appears on the skin later in childhood or adulthood, it is considered an acquired lesion, not a true birthmark. A birthmark is defined by its congenital or very early-onset developmental nature. New spots that emerge later in life are typically common acquired features like new moles, freckles, or sun spots.
It is important to monitor any existing birthmark or newly acquired spot for changes that might warrant medical attention. Any mark that begins to change rapidly in size, color, or shape should be evaluated by a healthcare professional.
Other concerning signs include irregular borders, the development of new symptoms like bleeding or itching, or a change in texture. While most birthmarks are benign, vigilance regarding changes in any skin mark is a sensible approach to skin health.