Summary
Psoriasis is a chronic skin disease that affects approximately 2–3% of the global population. It is characterized by an inflammatory state that manifests as scaly and itchy plaques on the skin. Omega-3 fatty acids, particularly DHA, have been shown to reduce levels of inflammation, suggesting potential therapeutic value in psoriasis management.
 
Introduction
Psoriasis is a chronic autoimmune condition of the skin that affects 2–3% of the global population. Environmental and genetic factors both contribute to psoriasis; the disease can flare up in response to triggers such as infection, stress, skin injury and diet.  Several forms of psoriasis exist: plaque, guttate, inverse, pustular, and erythrodermic psoriasis. The most common subtype is plaque psoriasis, which accounts for around 90% of all psoriasis cases. The condition presents as thickened, inflamed and itchy skin with overlying scales, usually located on the elbows, knees, scalp, and lower back. This can quite negatively affect a person’s quality of life from a sensory and aesthetic point of view. Mechanistically, psoriasis is characterized by increased levels of inflammation at the skin and an accelerated turnover of a specific cell type in the outermost skin layer called epidermal keratinocytes. In healthy individuals, these cells are continuously produced (in a process called cell proliferation) to replace the old layer of skin, supporting our skin barrier that protects us from pathogens and UV radiation. In persons with psoriasis, inflammation stimulates an overproduction of these cells, which outpaces the body’s ability to get rid of the old cell layer. This results in a buildup of dysfunctional keratinocytes, known as psoriasis plaques, which in turn promote inflammation.

A common way to assess the disease symptom presence is by the Psoriasis Area and Severity Index (PASI), scoring the number of body regions affected, the levels of redness, scaling and thickness, as well as the total area of affected skin per body region. Current treatment options such as steroid topical creams commonly target the overactive immune system in psoriasis, aiming to reduce levels of inflammation and restore the production speed of keratinocytes to a healthy pace. The anti-inflammatory properties of Omega-3 fatty acids EPA and DHA are known for their ability to counteract inflammation, regulate immune function, and improve skin barrier function. Perhaps unsurprisingly, clinical trials have shown that EPA and DHA play a positive role in protecting against psoriasis.
 
Research findings
In a study by Mysliwiec and fellow scientists, the levels of certain fatty acids in the serum of 85 patients with severe plaque psoriasis and 32 healthy controls were examined (Myśliwiec et al. 2017). Moreover, the BMI and psoriasis area severity index scores were assessed. With this, the authors aimed to assess the relationship between levels of certain circulating fatty acids, psoriasis risk and severity. The authors reported that compared to the healthy control group, psoriasis patients with a BMI under 30 had lower circulating levels of total Omega-3 fatty acids and DHA. Moreover, in all psoriatic patients, higher levels of circulating DHA and of total Omega-3 fatty acids were associated with a lower psoriasis area severity index score.
 
Morin and collaborators tested the effects of DHA on keratinocytes, the cell type that is prone to overproduction in psoriasis (Morin et al. 2021). The authors employed a tissue-engineered self assembly method to create a model that replicates psoriatic skin, allowing them to investigate the mechanistic effects of DHA. It was found that the addition of DHA to the keratinocytes reduced their abnormal proliferation properties characteristic of psoriasis. Crucially, the levels of inflammatory markers in the cells decreased as well following treatment with DHA. This study therefore showed that DHA acts on the two key mechanisms driving psoriasis, reducing characteristic disease hallmarks.  
 
In a randomized double-blind clinical trial by Tveit and colleagues, the effects of a DHA and EPA rich oil on psoriasis severity was investigated (TVEIT et al. 2020). A group of 64 men and women with psoriasis were evenly divided into groups receiving either a placebo or herring roe oil capsules containing a total of 1.9g DHA and 0,6g EPA every day for a period of 26 weeks. All participants were allowed to continue with any treatment that they were taking for their psoriasis symptoms. At the beginning and end of the supplementation period, psoriasis was assessed using the psoriasis area severity index. It was found that compared to the placebo group, the group receiving DHA and EPA supplementation showed a greater improvement in this index after the 26-week supplementation period. This improvement was the greatest in participants with moderate psoriasis (corresponding to index scores between 5.5 and 9.9). On the basis of these results, the authors concluded that supplements containing DHA and EPA may be considered by persons with psoriasis as adjunctive treatment.
 
Conclusion
Psoriasis is a chronic autoimmune skin condition, driven by inflammation and excessive production of skin cells called keratinocytes. This results in thickened, inflamed and itchy skin with overlying scales, often located on the elbows, knees, scalp, and lower back. DHA is known for its anti-inflammatory effects, which has been investigated in scientific studies and clinical trials on psoriasis. These have shown that DHA targets the key hallmarks of psoriasis in the skin cells affected by this disease, and can improve clinical outcomes. Persons with psoriasis who have higher relative circulating DHA levels seem to have lower psoriasis area severity index scores. Correspondingly, supplementation with DHA-rich oil improves psoriasis area severity index scores in psoriasis patients. On a cellular level, these findings are explained by the reported positive effects of DHA on keratinocyte proliferation and inflammation levels, defining features of psoriasis. Taken together, persons with psoriasis may consider to ensure they have sufficient intake of DHA to aid their management of psoriasis, given the positive effects reported in scientific literature.
 
References:
Morin, Sophie, Mélissa Simard, Nicolas Flamand, and Roxane Pouliot. 2021. ‘Biological Action of Docosahexaenoic Acid in a 3D Tissue-Engineered Psoriatic Skin Model: Focus on the PPAR Signaling Pathway’. Biochimica Et Biophysica Acta. Molecular and Cell Biology of Lipids 1866(12):159032. doi:10.1016/j.bbalip.2021.159032.

Myśliwiec, Hanna, Anna Baran, Ewa Harasim-Symbor, Piotr Myśliwiec, Anna Justyna Milewska, Adrian Chabowski, and Iwona Flisiak. 2017. ‘Serum Fatty Acid Profile in Psoriasis and Its Comorbidity’. Archives of Dermatological Research 309(5):371–80. doi:10.1007/s00403-017-1748-x.

TVEIT, Kåre Steinar, Karl Albert BROKSTAD, Rolf K. BERGE, Per Christian SÆBØ, Hogne HALLARÅKER, Stian BREKKE, Nils MELAND, and Bodil BJØRNDAL. 2020. ‘A Randomized, Double-Blind, Placebo-Controlled Clinical Study to Investigate the Efficacy of Herring Roe Oil for Treatment of Psoriasis’. Acta Dermato-Venereologica 100(10):5762. doi:10.2340/00015555-3507.