Psoriasis is an immune-mediated disease that causes raised, red, scaly patches to appear on the skin.
Psoriasis typically affects the outside of the elbows, knees or scalp, though it can appear on any location.
Some people report that psoriasis is itchy, burns and stings.
Psoriasis is associated with other serious health conditions, such as diabetes, heart disease and depression.
Type of psoriasis
There are five types of psoriasis. Learning more about your type of psoriasis will help you determine the best treatment for you.
Plaque psoriasis is the most common form of the disease and appears as raised, red patches covered with a silvery white buildup of dead skin cells. These patches or plaques most often show up on the scalp, knees, elbows and lower back. They are often itchy and painful, and they can crack and bleed.
Guttate [GUH-tate] psoriasis is a form of psoriasis that appears as small, dot-like lesions. Guttate psoriasis often starts in childhood or young adulthood, and can be triggered by a strep infection. This is the second-most common type of psoriasis, after plaque psoriasis. About 10 percent of people who get psoriasis develop guttate psoriasis.
Inverse psoriasis shows up as very red lesions in body folds, such as behind the knee, under the arm or in the groin. It may appear smooth and shiny. Many people have another type of psoriasis elsewhere on the body at the same time.
Pustular [PUHS-choo-lar] psoriasis in characterized by white pustules (blisters of noninfectious pus) surrounded by red skin. The pus consists of white blood cells. It is not an infection, nor is it contagious. Pustular psoriasis can occur on any part of the body, but occurs most often on the hands or feet.
Erythrodermic [eh-REETH-ro-der-mik] psoriasis is a particularly severe form of psoriasis that leads to widespread, fiery redness over most of the body. It can cause severe itching and pain, and make the skin come off in sheets.
It is rare, occurring in 3 percent of people who have psoriasis during their life time.
It generally appears on people who have unstable plaque psoriasis.
Where does psoriasis show up?
Psoriasis can show up anywhere—on the eyelids, ears, mouth and lips, skin folds, hands and feet, and nails. The skin at each of these sites is different and requires different treatments.
Light therapy or topical treatments are often used when psoriasis is limited to a specific part of the body. However, doctors may prescribe oral or injectable drugs if the psoriasis is widespread or greatly affects your quality of life. Effective treatments are available, no matter where your psoriasis is located.
Scalp psoriasis can be very mild, with slight, fine scaling. It can also be very severe with thick, crusted plaques covering the entire scalp. Psoriasis can extend beyond the hairline onto the forehead, the back of the neck and around the ears.
Facial psoriasis most often affects the eyebrows, the skin between the nose and upper lip, the upper forehead and the hairline. Psoriasis on and around the face should be treated carefully because the skin here is sensitive.
Treat sudden flares of psoriasis on the hands and feet promptly and carefully. In some cases, cracking, blisters and swelling accompany flares. Nail changes occur in up to 50 percent of people with psoriasis and at least 80 percent of people with psoriatic arthritis.
The most common type of psoriasis in the genital region is inverse psoriasis, but other forms of psoriasis can appear on the genitals, especially in men. Genital psoriasis requires careful treatment and care.
Inverse psoriasis can occur in skin folds such as the armpits and under the breasts. This form of psoriasis is frequently irritated by rubbing and sweating.
Studies have linked psoriasis and higher weight, but the causal relationship between the two has been unclear.
What triggers what?
Or could other underlying reasons explain the connection?
“Higher BMI may contribute to increased inflammation of the skin, which can exacerbate psoriasis, but it could also be that psoriasis leads to a person being less physically active and thus gaining weight,” explains Mari Løset.
She is a medical doctor at the Department of Dermatology at St. Olavs Hospital and a postdoctoral fellow at the Norwegian University of Science and Technology’s (NTNU) K.G. Jebsen Center for Genetic Epidemiology.
Løset is part of a team that been involved in a study of the causal relationship between BMI and psoriasis.
BMI stands for body mass index and is a measure of body fat content. It is calculated from a person’s height and weight.
The observational study is a large collaboration among researchers from NTNU, England and North America. Some of the data being used are from the Health Survey in Nord-Trøndelag (HUNT) and the UK Biobank.
Together, the analyses include data from 750 000 individuals.
Psoriasis is a chronic inflammatory condition of the skin, which causes a red, scaly rash.
The cause of the disorder is probably multifactorial, involving both heredity and the environment.
Worldwide, two to four per cent of the population is affected by psoriasis.
The incidence is particularly high in Norway.
“Self-reported data from two large population surveys in Norway indicate that six to eleven per cent of the population may be affected in this country,” says Løset.
A study in the city of Tromsø has shown that the incidence of psoriasis was 4.8 per cent in 1980, but had increased to 11.4 per cent in 2008.
“Similar studies from other parts of the world substantiate the fact that the condition is increasing,” says the postdoctoral fellow.
To investigate the causal relationship between BMI and psoriasis, the researchers used a method called Mendelian randomization. It is named after Gregor Mendel, who is known as the father of genetics.
According to Mendel’s principles of inheritance, whether we inherit a certain variant of genes from our mother or our father is random.
Genetic variants are randomly distributed, or randomized, between individuals.
“Mendelian randomization means that nature itself distributes individuals randomly into groups based on genes. This way, we can avoid the results being influenced by external factors,” says Løset.
“Our understanding of how genes are related to disease is increasing at record speed, and in this study we used known genetic variants as markers for BMI and psoriasis,” she adds.
By using Mendelian randomization, the researchers found that higher weight is a contributing factor to psoriasis.
They observed that greater BMI increased the chance of getting the disease.
“We calculated that the risk increased by nine per cent for each higher whole number on the BMI scale,” Løset says.
But the researchers are still uncertain about just how higher weight can lead to psoriasis.
“We still don’t know enough about the mechanisms behind this connection.
Fatty tissue is an organ that produces hormones and inflammatory signalling molecules, which could be a contributing factor,” says Løset.
So far, not much research has been done on whether weight loss can cause psoriasis to disappear, although a few clinical studies suggest the possibility.
“Psoriasis is a very complex disease and we hope to study subgroups, especially individuals with severe psoriasis.
The hypothesis is that we will be able to observe even greater links with higher weight,” says Mari Løset.
More information: Ashley Budu-Aggrey et al, Evidence of a causal relationship between body mass index and psoriasis: A mendelian randomization study, PLOS Medicine (2019). DOI: 10.1371/journal.pmed.1002739
Journal information: PLoS Medicine
Provided by Norwegian University of Science and Technology