DAN revisits and expands on the preventive measures for otitis externa
By Edward D. Thalmann, M.D., DAN Assistant Medical Director Captain, Medical Corps, U.S. Navy (retired)
The Alert Diver article on preventing otitis externa, or swimmers ear (see Can You Prevent Otitis Externa, or Swimmers Ear?), has generated a considerable number of commentaries from DAN members. This correspondence - both written and via telephone - has ranged from inquiries about "home brew" formulations to questioning whether recommending Otic Domeboro® Solution had some economic motivation.
First, DAN has absolutely no economic interest in any of the medications mentioned in the article. We named Otic Domeboro simply because it is the only solution tested by the Navy. However, there are others solutions which may work as well and turn out to be less expensive. Ask your pharmacist for recommendations.
When the Navy set out to tackle otitis externa in saturation divers, it did not want to use a "home brew": it needed a remedy that was pre-packaged, off-the-shelf, readily available, easy to use and one that worked. Otic Domeboro fit the bill; and the $1-per-day cost of preventing mission-compromising ear infections was insignificant considering the tens of thousands of dollars a day that many saturation dives cost.
The paper that inspired the choice of Otic Domeboro for the Navy otitis externa study was written by Dr. Edley H. Jones (Prevention of "Swimming Pool Ear." Laryngoscope 1971; 81:731-3). Dr. Jones began his observations back in 1924 at a local YMCA summer camp. He found that a saturated solution of boric acid in 90 percent ethyl alcohol prevented swimmers ear because the solution rapidly dried moist ear canals.
During the next 10 years he tried other solutions and found that 75 percent isopropyl alcohol worked as well. In 1938 someone contacted him with the information that the solution no longer worked. Upon investigation, however, Dr. Jones discovered that the user had not allowed the solution to remain in the canal long enough for the full dehydrating effect to work.
In 1961, Dr. Jones reported that five minutes of exposure to 5 percent acetic acid killed all bacteria normally found in the ear canal. He then judged that this would be an effective way to prevent swimmers ear, so he mixed some isopropyl alcohol with 5 percent acetic acid solution in several varieties to try at the camp. He found that 5 percent acetic acid in 85 percent isopropyl alcohol worked best. Adding a moisturizer (2 percent Alpha Keri oil) added nothing; and adding 10 percent propylene glycol (another moisturizer) caused the cells lining the ear canal to slough off, which was undesirable.
Other medical papers have stressed that it is the acidic pH that is the most important feature of solutions used for otitis externa. A 2 percent acetic acid solution has a pH of 3.0 and was found to drop the ear canal pH to 4-5: bactericidal to the normally found bacteria in the ear canal. (Otic Domeboro was chosen for the Navy study because the 2 percent acetic acid gave it the right pH and it also had drying agents.)
Making Your Own
So what's all this leading up to? "Home brew" to prevent ear infection, as many of our members wrote in to share with us. White wine vinegar is 4-6 percent acetic acid, and if it's mixed with an equal amount of isopropyl alcohol, it would probably work fine. Using undiluted vinegar may make the solution too acidic and cause irritation. Using less alcohol may be wise if you find that the 50:50 mix provides too much drying - this can make your ear canal sore after several days of use.
In principle, just diluting the acetic acid 50:50 with water might work since it appears that the acidic pH is more important than the drying effect of the alcohol. Adding propylene glycol or other moisturizers would seem either to be a waste of time in a home-brew, or it might produce undesirable effects according to Dr. Jones' observations.
Could lemon juice, which contains citric acid instead of acetic acid, be used instead if vinegar, as some members advised? In principle, if a solution was mixed to a pH of 3.0 it might, but whether other substances in lemon juice might promote bacterial growth I cannot say. For home brew I'd stick to what works - vinegar and isopropyl alcohol.
No matter what solution you use, remember its effectiveness is drastically reduced unless it remains in the ear canal a full five minutes. Another caution: the above solutions are for use in the otherwise normal ear with an intact eardrum. If there is any hint that the eardrum may be torn, do not use these solutions as they may cause damage to middle ear structures. And if any solution causes irritation, stop using it.
(c) July/August 1999 Alert Diver