How to Tell Aplasia Cutis Congenita from Birth Trauma

When you notice a mark or an open wound on your newborn’s head, it is completely natural to wonder if it is Aplasia Cutis Congenita (ACC) or a scrape caused during delivery, such as from forceps or a fetal scalp monitor. The main difference lies in how the skin itself is structured. ACC is a developmental condition where a specific patch of skin—including its normal layers and features like hair follicles and sweat glands—simply did not form during pregnancy ^[1][2]. In contrast, a birth injury is a tear, scrape, or bruise that occurs on skin that was completely and normally formed ^[3].

Because these two situations can look similar at first glance, parents and even some healthcare providers frequently confuse them. Understanding the difference can help ease unnecessary worry or misplaced blame regarding your delivery experience.

What to Look For in ACC

Aplasia Cutis Congenita is characterized by a “clean” absence of skin. If the spot is ACC, you may notice:

• Location: It is most commonly a single, well-defined, round or oval spot located on the top of the scalp (the vertex), often slightly off-center ^[4]. While less common, ACC can also occur on the trunk or limbs ^[5].
• Appearance: The area usually looks like a thin, smooth, shiny, or translucent membrane (atrophic skin) ^[6]. It may also look like a shallow ulcer or be covered by a scab (eschar) ^[7].
• Depth: Usually, ACC is shallow. In rare cases, the missing skin layers can extend deeper, potentially exposing underlying tissues or bone ^[6][8]. If this is the case, try not to panic—your medical team will carefully evaluate and protect the area with specialized dressings, and babies generally heal very well with proper management ^[9].
• Hair Collar Sign: ACC lesions are sometimes surrounded by a distinct ring of darker, longer hair known as the hair collar sign ^[10][11]. Because this can sometimes hint at an underlying connection to tissues beneath the skull, your doctor will likely recommend a painless imaging test, like an ultrasound, to safely evaluate the area ^[10].

What to Look For in a Birth Injury

Injuries sustained during a difficult delivery or from monitoring equipment look and behave like typical wounds.

• Location: The marks will usually correspond directly to where instruments were placed (for example, forceps marks on the sides of the head, or a tiny puncture from an internal fetal scalp monitor).
• Inflammation: Birth trauma is often accompanied by swelling, redness, inflammation, or bruising in the surrounding tissue ^[3][12].
• Healing Process: Over the first few weeks, a birth injury typically heals the way a normal scrape does—swelling goes down, a scab forms, and the skin repairs itself into normal tissue. If ACC presents as an open wound at birth, it will also go through a healing and scabbing process, which is why parents sometimes mistake it for a healing scrape ^[9]. The crucial difference is that ACC will heal into a permanent, hairless scar, rather than returning to fully normal, hair-bearing skin ^[13].

How Doctors Tell Them Apart

If there is uncertainty, your pediatric dermatologist or neonatologist can perform a painless, non-invasive exam using a dermatoscope (a specialized magnifying tool with a light).

When a doctor looks at ACC under a dermatoscope, the most important clue is a complete absence of follicular openings (the tiny pores where hair grows) because those structures never developed ^[14][15]. They may also see thicker-than-normal blood vessels visible through the thin top layer of the area ^[15].

In contrast, if a doctor examines a scrape from a birth injury, they will typically see hair follicles still present within or surrounding the injured tissue, even if there is temporary scabbing or inflammation over the top.

Whether your baby’s spot is an ACC wound or a birth injury, your healthcare team will provide you with specific daily care instructions. They will explain exactly how to keep the area clean, whether it needs to be covered, and which ointments to use ^[9]. Both conditions can be safely managed, allowing you to focus on bonding with your new baby.