Are Psoriasis and Allergies Linked?

Psoriasis is a common chronic multifactorial noncontagious autoimmune inflammatory disease that causes itchy or sore patches of thick, red skin with silvery scales. The impact of psoriasis on health is not only limited to the skin, but also influences multiple systems of the body, even mental health. It may happen at any age, including in childhood.

Psoriasis and allergies both stem from immune system irregularities. Psoriasis flares can result from skin injuries such as scratches, insect bites, vaccinations, and sunburn. Allergies can sometimes contribute to psoriasis flares. Itchy allergy hives can prompt a scratch response, which may lead to skin injury.

Allergic diseases, particularly atopic dermatitis, may be a risk factor for psoriasis. Patients with psoriasis have an increased prevalence of asthma and allergic rhinitis. Treating allergies may reduce psoriasis symptoms.

Comorbidities

Recently, psoriasis has been considered a systemic disease that can lead to many comorbidities. Psoriasis has shown correlations with cardiovascular disease, inflammatory bowel disease, diabetes mellitus, and depression.

Mast cells

Mast cells are immune cells located wherever antigens from the environment can enter the body, such as in the respiratory system, gastrointestinal tract, and skin. Mast cells contain granules that store inflammatory substances like histamine, cytokines, and heparin. Histamine release from mast cells can lead to hives in allergic reactions.

Sometimes mast cell activation can result in deeper and prolonged skin swelling that can cause skin issues like eczema or atopic dermatitis.

A 2017 study found that antihistamines reduced the itching intensity of psoriasis. The study found evidence to suggest that psoriasis mast cells could be functionally hyperreactive, and histamine might play a role in the development of psoriasis.

It was found in 2021 that mast cells are also active in psoriasis lesions, in contrast to their resting state in unaffected skin. Not only do mast cells become active in psoriasis lesions, but they also recruit other immune cells that produce inflammation.

Vitamin D

Both psoriasis and allergies may be linked to deficiencies in vitamin D. Vitamin D deficiencies may play a role in several conditions, including lung disease, respiratory infections, asthma, atopic dermatitis, and food allergies.

Vitamin D might regulate epigenetic changes that lead to allergic conditions. Vitamin D deficiency stems from a loss of nutrients resulting from the accelerated rate of skin shedding seen in psoriasis.

Vitamin D plays a critical role in psoriasis, and this is evidenced in many studies which reported either a deficiency or insufficiency of serum vitamin D in psoriatic patients. Several case-control studies have shown significant lower levels of serum 25(OH)D (the biologically active form of vitamin D) in psoriatic patients compared to controls and reported an inverse correlation between serum 25(OH)D and the severity of the disease.

Vitamin D supplementation may benefit people living with psoriasis by preventing conditions like high blood pressure and metabolic syndrome.

Psoriasis Triggers

Many people who are predisposed to psoriasis may be free of symptoms for years until the disease is triggered by some environmental factor. Common psoriasis triggers include infections, such as strep throat or skin infections, weather, especially cold, dry conditions, injury to the skin, such as a cut or scrape, a bug bite, or a severe sunburn, heavy alcohol consumption, certain medications — including lithium, high blood pressure drugs, nonsteroidal anti-inflammatory drugs (NSAIDs), and antimalarial drugs, and rapid withdrawal of oral or injected corticosteroids.

Risk Factors

Inflammatory bowel disease is a group of chronic conditions, including ulcerative colitis and Crohn’s disease, that cause inflammation and ulcers in the digestive tract.

Genetics may play an important role in the formation of psoriasis. Studies have found more than 60 genetic markers linked to Th17 cell activation, which is a key component of inflammation in psoriasis.

Around 40% of people with psoriasis or psoriatic arthritis have a family history of either condition.

Long-term smokers just about doubled their risk of psoriasis, when compared to those who’ve never smoked. Heavy smokers are two times as likely to have psoriasis.

Other risk factors for developing psoriasis include cardiovascular disease, metabolic syndrome, trauma to the skin, hypertension, diabetes, excessive alcohol consumption, infection, and obesity.

Symptoms

Psoriasis causes a buildup of skin cells on the skin’s surface. A skin cell typically grows and then falls off within 1 month. However, in psoriasis, skin cells grow in 3–4 days and pile up on the skin in plaques rather than falling off. This causes inflammation that may lead to itchy, uncomfortable, and sometimes painful lesions on the skin surface. This leads to thick plaques of skin that may be itchy, dry, and covered with silver, flaky skin (scales), pink-red in color, raised and thick.

Plaques are most often seen on the elbows, knees, and middle of the body. But they can appear anywhere, including on the scalp, palms, soles of the feet, and genitals.

Other symptoms may include joint or tendon pain or aching, nail changes, including thick nails, yellow-brown nails, dents in the nail, a lifting of the nail from the skin underneath, cyclic rashes that flare for a few weeks or months and then subside, small scaling spots (commonly seen in children), dry cracked skin that may bleed, and severe dandruff on the scalp.

A person’s symptoms may range from mild to severe depending on the type of psoriasis, the location, and the severity of symptoms. Mild psoriasis covers less than 3% of the body, moderate psoriasis covers 3–10% of the body, and severe psoriasis covers more than 10% of the body.

Complications

Psoriasis may develop into other health problems that could affect the bones, muscles, and metabolic system.

Complications of psoriasis include psoriatic arthritis, temporary skin color changes (post-inflammatory hypopigmentation or hyperpigmentation) where plaques have healed, eye conditions, such as conjunctivitis, blepharitis and uveitis, obesity, type 2 diabetes, high blood pressure, cardiovascular disease, other autoimmune diseases, such as celiac disease, sclerosis and the inflammatory bowel disease called Crohn's disease.

The occurrence of mental health comorbidities such as depression, anxiety, and low self-esteem is not uncommon in the context of psoriasis.