Strawberry marks visibility by 6 months
Only about 30% of hemangioma (strawberry mark) birthmarks are visible at birth; most develop between 4–6 weeks, and nearly all are visible by 6 months.
Snapshot · Stuff You Should Know
Selects: Birthmarks: Probably Not the Mark of the Devil
Explore episode
Jun 20, 2026
Where this was said
Port Wine Stains and Sturge-Weber Syndrome
At 15:35 · chapter starts 12:35
The conversation shifts to port wine stains, which the hosts treat as the most medically consequential vascular birthmark. Unlike macular stains, these don't fade — they can actually darken and become lumpy or scarred over time. More significantly, researchers investigating Sturge-Weber syndrome (a neurological condition present in about 6% of port wine stain cases) discovered a gene with a molecular switch permanently locked in the 'on' position, believed to be the culprit [1] — Josh Clark "Port wine stains are the only birthmark type with a partially identified genetic cause: a molecular switch permanently stuck in the 'on' po…" 20:40 . This makes port wine stains the only birthmark with a partially identified genetic cause. Josh explains the relationship carefully: having the birthmark doesn't mean you have the syndrome, but every Sturge-Weber patient has the birthmark.
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