THE CURE INDEX
Helio Cure's evidence score based on human clinical trials for red light therapy.
Smell disorders are conditions that reduce, distort, or block a person's ability to detect odors.
All 4 human studies on smell disorders reported the same thing: red light therapy helped, most often after COVID-19. With no contradictory results across 139 participants, the verdict is effective, and the CURE Index scored the condition at 86 out of 100, indicating strong confidence.
Red light therapy was associated with better smell on standard smell tests and on patients' own ratings. The 4 studies were 1 randomized controlled trial and 3 clinical trials, and all 4 reported effective outcomes.
Treatment centered on 660 nm, within a 660 to 808 nm range, in sessions of 40 seconds to 20 minutes, 5 to 12 times per week.
EVIDENCE AT A GLANCE
The numbers behind the verdict.
MOST CITED WAVELENGTH
The wavelength appearing most often in studies that showed benefit for smell disorders.
660 nmTREATMENT PROTOCOL RANGES
The lowest and highest values used across smell disorders studies.
| PARAMETER | RANGE |
|---|---|
| Wavelength | 660-808 nm |
| Session Duration | 40 seconds-20 minutes |
| Session Frequency | 5-12 per week |
Note: We have excluded meta-analyses and reviews from scoring, but the list of human studies below contains them for your reference.
5 Human Studies on Red Light Therapy for Smell Disorders
Review Found Light Therapy Effective for Post-COVID Smell Loss
Across 271 people in 10 human studies, a 2025 systematic review examined photobiomodulation (PBM) for lasting smell and taste loss after COVID-19. The included studies applied red and near-infrared light from 660 to 940 nm to the nose, and some also to the tongue, cheeks, and the glands that make saliva. The authors concluded that PBM appeared effective and improved aspects of quality of life, while calling for more high-quality, standardized trials.
- Study Type
- Review
- Participants
- 271
- Treated Area
- Nose And Mouth
- Wavelength(s)
- 660, 780, 808, 940 nm
- Distance
- Contact
- Session Duration
- 5 seconds, 9 seconds, 10 seconds, 40 seconds, 2 minutes, 3 minutes, 5 minutes
- Session Frequency
- 1, 5, 8, 10, 12, 16 per week
Study Title: Photobiomodulation in the management of persistent olfactory and gustatory dysfunction post-COVID-19: a systematic review.
Infrared Light Outperformed Red and Placebo for Post-COVID Smell
Standard smell-test scores rose 4.6 points more with infrared light than with a placebo in a 2025 randomized controlled trial of smell loss after COVID-19 in Brazil. 81 patients were split into a control group, a red 660 nm group, and an infrared 780 nm group, all also given the steroid prednisolone for 5 days and 90 days of smell training, with light applied inside the nose twice a week for 5 weeks. Response rates reached 68% in the infrared group, against 44% with red light and 26% in the control group. No major adverse events were reported.
- Study Type
- Randomized Controlled Trial
- Participants
- 81
- Treated Area
- Nose
- Wavelength(s)
- 660, 780 nm
- Distance
- 0.39 inches
- Session Duration
- 40 seconds
- Session Frequency
- 10 per week
- Therapy Duration
- 90 days
Study Title: Efficacy of the adjunctive use of photobiomodulation therapy in olfactory disorders in post-COVID-19 patients: A randomized controlled trial.
Brain Scans Showed Smell-Nerve Recovery After Laser Therapy
This 2023 study used brain scans to see whether low-level laser therapy (LLLT) could help with smell loss after a head injury in 24 patients. Those who completed 660 nm laser sessions on the smell-processing areas for 20 minutes over about 70 days were compared with untreated patients. Researchers found that the laser group showed more activity in several brain regions linked to smell, which they read as signs of nerve repair and rewiring, rather than a direct smell-test score.
- Study Type
- Clinical Trial
- Participants
- 24
- Treated Area
- Nose
- Wavelength(s)
- 660 nm
- Session Duration
- 20 minutes
- Therapy Duration
- 70 days
Study Title: The brain functional connectivity alterations in traumatic patients with olfactory disorder after low-level laser therapy demonstrated by fMRI.
Smell and Taste Improved After Nose and Mouth Light
A 2023 clinical trial tested photobiomodulation (PBM) inside the nose and mouth for smell and taste loss after COVID-19 in 20 people in Brazil. Patients received 660 nm light at 2 points inside the nose and 660 and 808 nm light at 3 points inside the mouth, across 12 sessions over 12 days. The trial found significant improvement in patients' own ratings of both smell and taste after treatment.
- Study Type
- Clinical Trial
- Participants
- 20
- Treated Area
- Nose And Mouth
- Wavelength(s)
- 660, 808 nm
- Session Frequency
- 12 per week
- Therapy Duration
- 12 days
- Study Scope
- Anosmia
Study Title: Can photobiomodulation restore anosmia and ageusia induced by COVID-19? A pilot clinical study.
All 14 Patients Regained Some Smell After Nasal Light
14 patients who lost their sense of smell after COVID-19 took part in a 2021 case series of photobiomodulation therapy (PBMT) in Brazil. Each received 660 nm light at 100 mW inside the nose for 3 minutes, delivering 18 J across one of 3 session schedules. Smell improved in all 14, though by differing amounts, and the authors appeared cautious, noting the study was small and had no comparison group.
- Study Type
- Clinical Trial
- Participants
- 14
- Treated Area
- Nose
- Wavelength(s)
- 660 nm
- Distance
- Near Contact
- Session Duration
- 3 minutes
- Session Frequency
- 5, 10 per week
- Therapy Duration
- 0, 5, 10, 2021 days
Study Title: Intranasal photobiomodulation therapy for COVID-19-related olfactory dysfunction: A Brazilian multicenter case series.
The CURE Index (Clinical Understanding of Red-light Evidence) by Helio Cure is a 0-100 evidence score based on published human clinical trials. Higher scores mean stronger evidence. Read full methodology →
Data is powered by AI and reviewed by the Helio Cure team.
This page is for educational purposes only. Not medical advice. Consult a healthcare provider before starting red light therapy. Helio Cure does not diagnose, treat, or cure any medical condition.
Last updated: Jul 29, 2026