Based on the affected frequency range and severity, sudden hearing loss can be categorized into four types: high-frequency, low-frequency, flat-type, and total hearing loss.

1. Low-frequency Type: Hearing loss occurs at frequencies of 1000 Hz and below, with a threshold elevation of ≥20 dB HL at least at 250 Hz and 500 Hz.

2. High-frequency Type: Hearing loss occurs at frequencies of 2000 Hz and above, with a threshold elevation of ≥20 dB HL at least at 4000 Hz and 8000 Hz.

3. Flat-type: Hearing is reduced across all frequencies, with an average hearing threshold (from 250 to 8000 Hz) ≤80 dB HL.

4. Total Hearing Loss (Profound): Hearing is significantly reduced across all frequencies, with an average hearing threshold (from 250 to 8000 Hz) ≥81 dB HL.