From the Guidelines

Nasal saline irrigation is advised for acute sinusitis, although the evidence is not strong.

The European Position Paper on Rhinosinusitis and Nasal Polyps 2020 1 suggests that nasal saline irrigation may be beneficial, but the evidence is of very low quality, and no strong advice can be given.
Another study from the same year 1 found that 20 out of 33 studies reported a positive effect of nasal saline irrigations on clinical outcomes in adult chronic rhinosinusitis, but the studies were very different in design and outcome measurements.
The American College of Physicians and the Centers for Disease Control and Prevention 1 suggest that adjunctive therapy, such as intranasal saline irrigation, has been shown to alleviate symptoms and potentially decrease antibiotic use.

The evidence for nasal saline irrigation in acute sinusitis is limited and of low quality.
Despite this, nasal saline irrigation may be beneficial in alleviating symptoms and is considered a low-risk treatment.
More studies are necessary to further analyze the effectiveness of nasal saline irrigation in acute sinusitis.
In clinical practice, nasal saline irrigation can be considered as part of supportive care for patients with acute sinusitis, along with other symptomatic relief measures such as analgesics and antipyretics.

From the Research

The use of nasal saline irrigation (SNI) in the treatment of acute sinusitis is a topic of ongoing debate 2.
Some studies suggest that SNI may be beneficial in improving symptoms and quality of life for patients with acute sinusitis, particularly in children 3, 4.
A study published in the International Journal of Pediatric Otorhinolaryngology found that normal saline nasal irrigation significantly improved symptoms and quality of life in children with acute sinusitis 3.
Another study published in the Journal of Microbiology, Immunology, and Infection found that nasal irrigation with normal saline was an effective adjunctive treatment for acute sinusitis in atopic children 4.
However, a Cochrane review found that the evidence for the efficacy of saline nasal irrigation in treating acute upper respiratory tract infections, including acute sinusitis, was limited and inconclusive 5.
The American Family Physician journal notes that evidence on the use of saline nasal irrigation for the treatment of acute rhinosinusitis is poor, but it may be used to treat symptoms within the first 10 days of upper respiratory infection 6.

The use of nasal douches with isotonic and hypertonic saline solutions is recommended for patients with acute sinusitis, although the evidence is limited 2.
It is essential to clean the nasal douche thoroughly and use the proper salt concentration (2-3.5%) to prevent infections 2.
Nasal saline irrigation may be considered as an adjunctive treatment for acute sinusitis, particularly in children and atopic patients, but more research is needed to confirm its efficacy 3, 4, 5.