Asked by: Lori Sautter, USA
An adult head weighs between 5kg and 6.3kg. Your neck muscles could cope with more weight, but an abnormally large head is usually a sign that something else is wrong.
Proteus syndrome, for example, is caused by an extremely rare mutation in the AKT1 gene, right at the start of embryonic development. This causes excessive bone and tissue growth, and depending where the affected cells end up, it can cause a wildly oversized head.