The researchers found that people with rosacea had an increased risk of dementia - particularly Alzheimer's disease.
Researchers in Denmark who came to this conclusion also highlight that the risk is highest in older patients and those whose skin complaint was diagnosed by a hospital dermatologist.
The team carried out the study because there is evidence rosacea is associated with higher levels of certain proteins that have also been implicated in various brain-wasting disorders, such as Alzheimer's disease and other forms of dementia. The proteins include matrix metalloproteinases and antimicrobial peptides.
In the Annals of Neurology, the researchers explain how they investigated the link between rosacea and dementia from data in Danish registers covering the period 1997-2012, when there were nearly 6 million Danish citizens aged 18 and over, including nearly 83,500 patients with rosacea.
The individuals were followed up to the end of 2012, or until they left Denmark, and were diagnosed with dementia, or died - whichever came first. Altogether, just over 99,000 developed dementia, including around 29,000 who were diagnosed with Alzheimer's disease.
When they analyzed the data, the researchers found that compared with patients who did not have the skin complaint, those with rosacea had a 7 percent increased risk of dementia and a 25 percent increased risk of Alzheimer's disease, with older people at the higher risk end.
For women, the raised risk of Alzheimer's linked to rosacea was 28 percent, whereas for men with the skin disorder it was 16 percent.
'Prominent neurological, neuropsychiatric symptoms' for some patients
When they limited the analysis to cases of rosacea that had been diagnosed by a hospital dermatologist, the researchers found the increased risk of dementia and Alzheimer's disease were 42 percent and 92 percent, respectively.
Fast facts about rosacea
- Rosacea affects millions of Americans
- There are no cures for the condition, but some medicines can alleviate symptoms
- Rosacea is often mistaken for eczema, acne, or some other skin condition.
First author Dr. Alexander Egeberg, of the Department of Dermato-allergology at Herlev and Gentofte Hospital, University of Copenhagen, says:
"A subtype of patients have prominent neurological symptoms such as burning and stinging pain in the skin, migraines, and neuropsychiatric symptoms, suggesting a link between rosacea and neurological diseases."
"Indeed," he continues, "emerging evidence suggests that rosacea may be linked with neurological disorders including Parkinson's disease and now also Alzheimer's disease."
Dr. Egeberg urges rosacea patients not to assume that having the skin condition means they will develop dementia.
He explains there are certain underlying mechanisms that rosacea and Alzheimer's disease appear to share, and this may explain the link, but we do not know whether one causes the other.
He and his colleagues suggest doctors should look out for symptoms of cognitive dysfunction in older patients with rosacea, and that only further studies can reveal if treating rosacea may also modify patients' risk of developing dementia.