Psoriasis is an inflammatory, immune-mediated disease that causes a skin rash. Allergies may trigger psoriasis due to a scratching-related skin injury. Differences between psoriasis and a hives rash can help identify the conditions.

An immune-mediated condition is one in which inflammation occurs due to the immune system not functioning properly. Both psoriasis and allergies result from immune system dysregulation, but the conditions are not the same.

Psoriasis is a chronic condition in which the immune system overreacts, causing skin cells to multiply too quickly and form a scaly rash. Some experts believe that infection-fighting cells mistakenly attack healthy cells.

Allergies occur when the immune system overreacts to allergens, such as pollen or dust mites. The result is symptoms that can include:

  • a runny nose
  • wheezing
  • rash

This article reviews the connection between allergies and psoriasis, along with how to tell the difference between them and treat each condition.

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Allergies can sometimes contribute to psoriasis flares.

Itchy allergy hives can prompt a scratch response, which may lead to skin injury. Psoriasis flares can result from skin injuries such as:

  • scratches
  • insect bites
  • vaccinations
  • sunburn

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
  • 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 2021 study found 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.

A 2015 study found that vitamin D deficiencies may play a role in several conditions, including:

  • lung disease
  • respiratory infections
  • asthma
  • atopic dermatitis
  • food allergies

The study authors theorize that vitamin D might regulate epigenetic changes that lead to allergic conditions.

Severe psoriasis may lead to a vitamin D deficiency, according to a 2017 study. Study authors theorize that the vitamin D deficiency stems from a loss of nutrients resulting from the accelerated rate of skin shedding seen in psoriasis.

Experts believe that the relationship between low vitamin D and psoriasis might work in both directions and that a preexisting deficiency in vitamin D might also be a contributing factor that leads to psoriasis.

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

It is best for a person to discuss taking vitamin D supplements with their doctor, as too much vitamin D may lead to adverse health effects.

Seasonal allergies have a range of symptoms:

  • Nasal symptoms: Sneezing, runny nose, and congestion are common allergy symptoms, as well as itchy eyes, nose, and mouth.
  • Asthma symptoms: Wheezing and shortness of breath are examples of asthma symptoms that are linked to allergies.
  • Cough: An allergy cough might be dry and chronic, or it might occur more frequently in certain environments or during specific seasons.
  • Fatigue: When allergy symptoms interfere with sleep, it may lead to fatigue.
  • Headaches: Migraine attacks and sinus headaches are linked to allergies.
  • Rash: Hives, bumps, redness or discoloration, and itching are features of an allergic rash.

Fever is not a seasonal allergy symptom. If other allergy symptoms occur with fever, they might have another cause, such as infection.

Psoriasis can appear in different forms and on various parts of the body. Symptoms can include:

  • plaques, which are scaly lesions on the skin
  • nail dents or pits
  • pus-filled blisters
  • skin worn into smooth patches in areas where there is friction
  • a rash over the entire body that can cause fever and dehydration

The whole-body rash known as erythrodermic psoriasis is serious and requires medical attention.

Psoriasis and allergy hives have similar characteristics. Both can cause itching and can be widespread or confined to one area of the body.

However, there are differences between a psoriasis rash and hives from allergies that can help identify the two conditions.

scaly, dry, or cracked skinflat and smooth rash
appears graduallyappears quickly, within minutes
lasts for several weeks or moreintermittent and may disappear within hours
sometimes bleedsonly bleeds when scratched excessively

Hives are more common than psoriasis, which affects only around 3% of adults in the United States, according to research published in 2021. Hives, on the other hand, affects an estimated 20% of people at some point in their life.

If a person suspects they have hives or psoriasis, a doctor can use a physical exam, health history, and sometimes a skin sample analysis to confirm a diagnosis.

Treating allergies can sometimes soothe psoriasis symptoms.

Antihistamines are commonly used to treat allergies. A 2017 study found that antihistamines also reduced the itching intensity participants with psoriasis experienced.

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.

Allergy treatments

Treating allergy itchiness can also prevent psoriasis from worsening.

The American Academy of Dermatology Association recommends against scratching allergy hives because this can trigger a psoriasis flare. Instead, people living with allergy itch are advised to consider using skin-calming techniques such as:

  • applying an ice pack or cool, wet cloth to the itchy area
  • moisturizing skin
  • taking an oatmeal bath
  • applying cooling agents like calamine or menthol
  • using a topical anesthetic containing pramoxine

Psoriasis treatments

Psoriasis treatment includes topical, oral, or injectable medications such as:

  • corticosteroids
  • medications containing vitamin D
  • retinoids
  • tar products
  • immunosuppressants
  • biologics

Doctors sometimes use phototherapy to treat psoriasis when the rash covers a large area.

As well as skin injury from an allergy, other possible psoriasis triggers include:

  • excess alcohol consumption
  • smoking
  • stress
  • hormonal changes
  • throat infection
  • immune conditions such as HIV
  • certain medications such as:
    • ACE inhibitors
    • ibuprofen and other anti-inflammatory medications
    • lithium
    • some antimalarial medications

Here are some frequently asked questions about psoriasis.

Do antihistamines help psoriasis?

Antihistamines may reduce itchiness associated with psoriasis.

Can pollen cause psoriasis flare-ups?

Pollen commonly triggers seasonal allergies. If a person scratches their skin due to an itchy allergic reaction, this can cause a skin injury. This in turn may trigger or worsen psoriasis.

Why am I getting psoriasis all of a sudden?

Exposure to a trigger can cause a sudden psoriasis flare-up. Examples of triggers include stress, alcohol, smoking, infection, and hormonal changes.

Psoriasis and allergies both stem from immune system irregularities.

For some people, allergies can trigger psoriasis flares. Skin injury from scratching allergy hives is one reason for this connection.

Treating allergies may reduce psoriasis symptoms. Antihistamine can help reduce itching related to both allergies and psoriasis.