Hearing Loss in One or Both Ears

Hearing loss can affect one or both ears. 

Hearing loss can be approximately the same in each ear, or worse in one ear than the other.

Hearing loss from environmental causes like noise, ototoxic drugs, and aging are generally symmetrical (both ears).

Very often Industrial noise is the concentration of the low frequencies and industrial workers spend most of the time in a reverberant environment. Our head and body do not work as a shadow for the low-frequency noise.  So, the noise from the right side bounces from the left wall with minimum loss and becomes the same loud as the left side.

 Hearing loss from medical causes like infection, mumps, the tumor is often asymmetrical (one ear)³.

Drivers usually have a hearing loss in the left ear due to noise exposure from an open window on the left side.

Music contents of significant amount high-frequency energy in a non-reverberant environment. Asymmetry of 25 dB is quite common for musicians especially violin players⁴. 

Gun short is performing in a non-reverberant environment. Hunters have hearing loss in the ear opposite to their dominant hand.