Is hypochlorous acid (HOCl) effective for treating smell disorders such as hyposmia or anosmia?

Hypochlorous Acid for Smell Disorders: Evidence and Recommendations

Hypochlorous acid (HOCl) has limited evidence supporting its effectiveness for treating smell disorders such as hyposmia or anosmia, and is not currently recommended as a first-line treatment for these conditions.

Current Evidence for HOCl in Smell Disorders

The evidence regarding hypochlorous acid for treating smell disorders is limited:

• One study examined low concentration hypochlorous acid as a nasal irrigation solution and found it had antimicrobial properties against various bacteria, fungi, and viruses without showing toxicity to human nasal epithelial cells 1. However, this study did not specifically evaluate its effects on smell disorders.

• The European Position Paper on Rhinosinusitis and Nasal Polyps 2020 mentions one double-blind placebo-controlled trial (Yu 2016) that used low-concentration HOCl versus saline in chronic rhinosinusitis patients. While it showed significantly reduced SNOT-20 scores at 2 and 4 weeks, the study did not specifically focus on olfactory outcomes 2.

Recommended Approaches for Smell Disorders

Based on current guidelines, the following treatments have stronger evidence for smell disorders:

First-Line Treatments:

1. Olfactory training

   • Recommended by multiple guidelines for post-infectious olfactory dysfunction 2, 3
   • Involves repeated exposure to different odors to stimulate olfactory nerve regeneration

2. Topical corticosteroids

   • Supported by systematic reviews and randomized controlled trials 3
   • Particularly useful when inflammatory components are present

Assessment and Diagnosis:

Before initiating treatment, proper assessment is crucial:

• Determine the cause of smell disorder (post-viral, post-traumatic, sinonasal disease, etc.)
• Distinguish between hyposmia (decreased smell), anosmia (absence of smell), or dysosmia (distorted smell) 4
• Consider duration of symptoms and associated conditions

Treatment Algorithm:

1. For post-infectious olfactory dysfunction (including post-COVID):

   • Start with olfactory training
   • Consider adding topical corticosteroids if inflammation is suspected
   • Monitor for at least 3 months before changing approach 3

2. For chronic rhinosinusitis-related olfactory dysfunction:

   • Address underlying sinonasal inflammation with appropriate treatments
   • Topical corticosteroids are particularly beneficial in this group

Cautions and Considerations

• Avoid intranasal zinc preparations, which have been associated with permanent anosmia 5
• MRI imaging is generally not indicated unless there are other concerning neurological symptoms or no clear temporal relationship to a viral infection 2
• Most post-viral olfactory dysfunction shows some improvement over time, though complete recovery is not guaranteed

Conclusion

While hypochlorous acid has demonstrated antimicrobial properties that could theoretically benefit certain nasal conditions, there is insufficient evidence to recommend it specifically for treating smell disorders. Olfactory training and topical corticosteroids remain the best-supported interventions for most cases of hyposmia and anosmia, particularly those of post-infectious origin.