Surfer's ear is the common name for an exostosis or abnormal bone growth within the ear canal. They are otherwise benign hyperplasias (growths) of the tympanic bone thought to be caused by frequent cold-water exposure. Cases are often asymptomatic. Surfer's ear is not the same as swimmer's ear, although infection can result as a side effect.

Irritation from cold wind and water exposure causes the bone surrounding the ear canal to develop lumps of new bony growth which constrict the ear canal. Where the ear canal is actually blocked by this condition, water and wax can become trapped and give rise to infection. The condition is so named due to its high prevalence among cold water surfers, although it can occur in any water temperature due to the evaporative cooling caused by wind and the presence of water in the ear canal.

Most avid surfers have at least some mild bone growths, causing little to no problems. The condition is gradually progressive and can generally be prevented by shielding the ear from water by consistently using earplugs and wetsuit hoods. The condition is not limited to surfing and can occur in any activity with cold, wet, windy conditions such as windsurfing, kayaking, sailing, jet skiing, kitesurfing, and diving.

In general, one ear will be somewhat worse than the other due to the prevailing wind direction of the area surfed or the side that most often strikes the wave first. Common symptoms include recurrent otitis externa, obstructed sensation, conductive hearing loss, pain in the ear, and tinnitus.

The majority of patients present in their mid-30s to late 40s. This is likely due to a combination of the slow growth of the bone and the decreased participation in activities associated with surfer's ear past the 30s. However, surfer's ear is possible at any age and is directly proportional to the amount of time spent in cold, wet, windy weather without adequate protection.

The normal ear canal is approximately 7 mm in diameter and has a volume of approximately 0.8 ml (approximately one-sixth of a teaspoon). As the condition progresses, the diameter narrows and can even close completely if untreated, although people generally seek help once the passage has constricted to 0.5–2 mm due to the noticeable hearing impairment. While not necessarily harmful in and of itself, constriction of the ear canal from these growths can trap debris, leading to painful and difficult to treat infections.

A 2015 review of eight other studies found that the prevalence of surfer's ear among surfers ranged from 31% to 80%, largely depending on sea temperature of the geographical area studied, with colder climates having higher prevalence. The study also found among 105 surfers in Cornwall, England 63.8% had surfer's ear.

The widespread use of wetsuits has allowed people to surf in much colder waters, which has increased the incidence and severity of surfer's ear for people who do not properly protect their ears. Preventative measures include avoiding activity during extremely cold or windy conditions, and keep the ear canal as warm and dry as possible through the use of earplugs and wetsuit hoods. In one study, two thirds of 92 surfers were aware that surfer's ear could be prevented. One study suggests that for kayakers, since surfer's ear is a slowly progressive condition, kayakers may not wear earplugs until symptoms appear.