Denmark: Smoking as a causal factor in the development of psoriasis is not completely understood. Using observational analyses, a study published in Frontiers in Immunology revealed smoking as an independent risk factor for moderate to severe psoriasis.
In the study using genetic and observational data from more than 100,000 individuals from the adult Danish general population, the researchers found that smoking is observationally associated with a 2.5-fold higher risk of moderate to severe psoriasis in prospective analyses.

Psoriasis is a chronic skin condition that affects millions of people worldwide. It is characterized by red, scaly patches that can be itchy and painful. While psoriasis's exact cause is unknown, several risk factors have been identified, including smoking.
In a recent study, Dr. Charlotte N. Koch, and a team of doctors from Copenhagen, Denmark, aimed to determine whether smoking is an independent and causal risk factor for psoriasis. The researchers used a Mendelian randomization design. This approach uses genetic variants as proxies for modifiable exposures, thereby avoiding confounding and reverse causation.
The study included data from the Copenhagen General Population Study, which included 105,912 individuals with full information on lifestyle factors, biochemistry, and genotype data. Of these individuals, 1,240 cases of moderate to severe psoriasis were included in the analysis. The researchers used the genetic variant CHRNA3 rs1051730, strongly associated with high lifelong cumulative smoking, as a proxy for smoking.
The study revealed the following clinical takeaways:
In observational analyses, the study showed that smoking was an independent risk factor for moderate to severe psoriasis.
Using CHRNA3 rs1051730 as a proxy for smoking, the researchers did not find this association causal.
The odds ratio of developing moderate to severe psoriasis was 1.05 per T-allele in every smoker, indicating that the genetic variant was not strongly associated with psoriasis risk.
The findings of this study have important implications for public health. While smoking is still associated with an increased risk of psoriasis, this study suggests that the relationship may not be causal. This information can help inform smoking cessation efforts for individuals with psoriasis and guide future research on the underlying mechanisms of the condition.
“While smoking remains a significant risk factor for psoriasis, more research is needed to fully understand the complex interplay between genetics, lifestyle factors, and disease development”, added the study's authors.
Reference:
Näslund-Koch C, Vedel-Krogh S, Bojesen SE and Skov L (2023) Smoking is an independent but not a causal risk factor for moderate to severe psoriasis: A Mendelian randomization study of 105,912 individuals. Front. Immunol. 14:1119144. doi: 10.3389/fimmu.2023.1119144