Evening primrose oil, as well as borage oil, did not ease the itchy, red skin of patients with eczema any better than placebo medicines, a recently published study found.
The researchers said that the findings do not justify future research into the oils, as their results are consistent with those of previously published studies.
"Talk to your dermatologist about eczema treatments."
Eczema, or atopic dermatitis, emerges during childhood and has no known cure. The skin condition affects about 10 to 20 percent of school age children.
Researchers, led by Joel Bamford, MD, from the Department of Family Medicine and Community Health at the University of Minnesota Medical School and Essentia Health System in Duluth, Minnesota, investigated whether primrose and borage oil eased eczema symptoms.
Evening primrose oil, drawn from the evening primrose plant, is taken orally to treat osteoporosis and breast pain. Borage oil from the borage plant works similarly to primrose oil.
The researchers looked at 27 studies published through August 2012 that involved almost 1,600 adults and children from 12 countries who were diagnosed with eczema.
The studies assessed how well the two different oils eased eczema symptoms. Of the included studies, 19 investigated primrose oil and the rest looked into borage oil.
In seven of the studies, participants and doctors both reported that evening primrose oil did not visually improve their global eczema symptoms.
Patients and doctors also reported that borage oil did not significantly improve eczema compared to using a fake treatment, or placebo.
"Oral borage oil and evening primrose oil appear to be equivalent in their lack of effect on eczema," the researchers wrote in their report. "They had the same effect on global ratings as the placebos used. They do not seem to add any benefit to eczema as measured in this systematic review."
Both oils caused the same mild, fairly common short-term side effects, including upset stomach, diarrhea and headache.
One report stated that primrose oil taken longer than a year could lead to inflammation, blood clots and suppression of the immune system.
The researchers did not find evidence of harm in the short-term trials, nor did they investigate how the oils affected patients in the long-term.
Dr. Bamford and colleagues noted that the way in which each of the studies reported its results varied from study to study. The researchers were not able to determine how the oils affected other factors such as cost and quality of life.
Also, the number of people included in each of the studies was small on average and some of the data may have been missing. The researchers determined that the majority of studies had a low bias risk.
The study was published online April 29 in The Cochrane Library. No outside funding was received for the study.
One of the authors received a grant from the Miller-Dawn Foundation and was repaid by the Effamol Pharmeceutical company, which supplied the medication, blood testing and fake medicines.