What causes osteoma/exostosis in the external auditory canal?

Osteoma or exostosis in the external auditory canal is mainly associated with environmental factors, particularly prolonged exposure to cold water, which often affects individuals who engage in water sports. This condition is characterized by the growth of bone in response to prolonged irritation or stress; in this case, the continuous exposure to cold water can lead to the formation of new bone in the canal as a protective response.

This growth typically manifests as bony protrusions within the ear canal, and it is commonly seen in surfers and divers. The relationship between exposure to cold water and bone growth is well recognized in medical literature, making this the most plausible cause among the options provided.

Other factors, like infections in the ear or allergic reactions, do not typically lead to the development of osteomas or exostoses. Instead, they can cause different ear conditions, but not the bone growth seen in osteoma/exostosis. Genetic predisposition may have some influence on various bone growth diseases, but it is not specifically linked to the formation of osteoma/exostosis in the external auditory canal in the same direct manner as prolonged cold water exposure.