Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Total 1100
Physiological - Other
Flight Deck / Cabin / Aircraft Event Illness / Injury; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
General Flight Cancelled / Delayed; General Work Refused
Aircraft
During preflight; the APU was started and the packs were turned on. Shortly after APU air was initiated; a foul smell began to emanate from the ECS. The smell was a strong body-odor/burnt onion odor. After some time; my eyes began to burn and I developed a slight headache. The odor did not get better; it only got worse. When it was determined we were experiencing a fume event; the CA immediately stopped boarding; de-planed; and maintenance took the aircraft out of service. All agencies were notified (Ramp; Ops; Mx; Flight Leadership). The entire crew went to the ZZZ clinic to get checked out. I was rescheduled to operate a later flight to ZZZ1 after the event. However; after being seen by the clinic physician and in the interest of flight safety; I chose not to operate the re-scheduled leg.
B737-800 First Officer reported a fume event during boarding resulting in flight cancellation and entire flight crew received medical evaluation due to physiological symptoms.