B737-800
Flight Crew Air Transport Pilot (ATP)
Physiological - Other
Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Illness / Injury; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew Returned To Gate; General Flight Cancelled / Delayed; General Physical Injury / Incapacitation
Aircraft
After engine start and during taxi both the Captain and First Officer smelled a strong odor of dirty socks in the cockpit. We started to feel light headed and nauseous. I donned my oxygen mask. I checked with the flight attendants and they did not smell anything. We returned to the gate. We went to the hospital.
After push back and normal start of #2 engine; ground crew disconnected and CA instructed me to start #1. Engine #1 started normally. After start/taxi checks completed and the takeoff checklist initiated; we received taxi instructions; and began to roll. That's when I first recognized an unpleasant odor and made a comment to the CA. We continued taxi for another minute or two and the CA asked me if I smelled dirty socks. I replied yes; and the CA decided to return the gate; we coordinated with Ground to return and the CA put his O2 mask on. I elected to open the FO side window as we were still fairly close to terminal and wanted better communications. We elected to start the APU and turn off Engine Bleed air. We returned to a different gate than we departed from in another terminal after coordination with Ops. We didn't feel as well as we had previously; both pilots experiencing some nausea and headache. We notified station personnel and they helped coordinate our transport to the hospital for further evaluation.
B737 flight crew reported a dirty sock smell after beginning to taxi for takeoff. The flight returned to the gate and the pilots were transported to a hospital.