Hi thanks for using HCMRedness
and crust formation shows some inflammation behind ear. which needs to be examined by a doctor.
It could be a infection of hair follicle or enlarged lymph node
or infection with in ear presenting as abscess
.consult ENT specialist
for ear examination .
you may need to apply antibiotic cream topically. any infection in ear needs to be treated.
Hope I have answered your query. wish your son a good health.