What Is the Hair Collar Sign in Aplasia Cutis Congenita?

The hair collar sign is a ring of darker, longer, or coarser hair that surrounds a bald patch or scalp lesion on a newborn’s head ^[1]. In the context of aplasia cutis congenita (ACC)—a condition where a baby is born missing a patch of skin, usually near the crown or midline of the scalp—doctors view this unique pattern of hair growth as an important clinical signal ^[1][2].

While hearing that doctors need to investigate further can be terrifying for a new parent, it is important to know that for many babies, the underlying structures are perfectly normal ^[3][4]. The skin simply needs time and gentle care to heal. However, because this specific hair pattern can suggest that the skin defect connects to deeper areas, doctors must be cautious and run necessary tests before confirming the area is safe ^[2].

What Does the Hair Collar Sign Look Like?

If your baby has a hair collar sign, you will typically notice a distinct halo or ring of thick, dark, and coarse hair immediately bordering the area of missing skin (the ACC lesion) ^[1]. This ring of hair stands out because it is often much darker and longer than the rest of the baby’s normal scalp hair. The bald patch in the center might look like a thin, shiny membrane, an open sore, or a small bump ^[5].

Why Do Doctors Investigate Further?

During fetal development, the skin, skull, and brain form in overlapping layers. Sometimes, the layers do not close completely over the center of the head, leading to a developmental difference known as cranial dysraphism ^[2][6].

The hair collar sign serves as a warning that the surface skin defect might not be an isolated surface issue, but could instead be linked to deeper structures:

• Skull bone gaps: The bone beneath the bald patch may be thin or missing entirely ^[4][7].
• Brain or meningeal connections: There may be a small channel connecting the skin to the brain or the protective membranes surrounding the brain (meninges) ^[2].
• Vascular differences: There could be unusual clusters of blood vessels underneath the patch ^[5].

What if a connection is found?
If imaging reveals a connection to the brain or skull, it does not automatically mean your baby will have brain damage or developmental delays. Many of these connections can be safely and permanently repaired by a pediatric neurosurgeon, and with early intervention, the long-term outlook for these children is often excellent ^[3][7].

Protecting the Area Right Now

Because of these potential deeper connections, it is crucial to protect the area while waiting for imaging. The medical team must not biopsy, puncture, or surgically alter the lesion without further investigation, as doing so could inadvertently injure underlying tissue or introduce a serious infection ^[2][7].

• Handle with care: Protect the bald patch from being scratched, picked, or bumped by hats, clothing, and fingernails.
• Advocate for your baby: Remind nurses and care providers that the area is a suspected hair collar sign and should only be gently cleansed according to your doctor’s exact instructions.

Next Steps and Recommended Imaging

If your baby’s doctor identifies a hair collar sign, the next step is diagnostic imaging to see beneath the skin and skull ^[2].

• Cranial Ultrasound: This is often the first step because it is quick, painless, and can be done easily at the bedside ^[8]. It uses sound waves to check for obvious gaps in the skull.
• Magnetic Resonance Imaging (MRI): An MRI is considered the gold standard for evaluating a hair collar sign ^[8][9]. It provides superior, highly detailed pictures of the brain and soft tissues, allowing doctors to detect subtle connections that an ultrasound might miss ^[9][5].

Will my newborn need sedation for the MRI?
Many parents worry about putting their newborn to sleep for an MRI. Fortunately, most hospitals use a non-pharmacological technique called “feed and swaddle” (or “feed and bundle”) for infants ^[10][11]. By feeding your baby right before the scan and wrapping them snugly in a blanket, they can usually fall into a deep, natural sleep, avoiding the need for anesthesia or sedating medications entirely ^[12][13].

Once imaging is complete, a multidisciplinary team—often including a pediatric dermatologist, a neonatologist, and a pediatric neurosurgeon—can safely determine the best way to care for your baby’s scalp ^[3].