What Is Actinic Prurigo?

Actinic prurigo is a rare genetic disease that causes the skin to develop small, intensely itchy, red and inflamed hard lesions upon sun exposure. The rash resembles atopic dermatitis (eczema); however, the lesions mainly develop more in sun-exposed areas as opposed to the folds of the skin that are typical in eczema.¹ 

Overview

Actinic prurigo (AP) may also be referred to as prurigo, hydroa aestivale or Hutchinson summer. It is a rare skin condition that is caused by an allergic reaction to sunlight (actinic is Greek for ‘sunlight’). It is believed to be an autoimmune, genetic disease as certain genes have been shown to cause the immune system of actinic prurigo patients to ‘‘overreact’’ when exposed to sunlight.

Actinic prurigo results in a skin rash which typically presents itself in the form of intensely itchy, solid lesions (‘prurigo’) mainly on sun-exposed areas including the face, neck and extremities.¹  

Actinic prurigo can occur anytime during the year, but it is more likely to manifest and worsen during the early spring and summer months due to the more direct and intense sunlight.¹ 

Causes of actinic prurigo

Actinic prurigo (AP) is mainly caused by exposure to the long- (UVA) and short- (UVB) wave ultraviolet (UV) rays from sunlight. However, how and why UV light causes this abnormal skin reaction remains unclear to this day.

Current research suggests that AP has a strong genetic cause as over 60% of the reported cases have a common allele (specific form of a gene) of one subtype gene called the human leukocyte antigen (HLA) DR4 allele. 

Additionally, people with moderate to severe AP have been demonstrated to have high levels of immunoglobulins (antibodies), suggesting that UV light (from both UVA and UVB) triggers an allergic immune response by the immune system. This involves the immune system producing too many antibodies and other immune cells that aggravate the skin and result in the appearance of lesions.¹

Signs and symptoms of actinic prurigo

An intensely itchy rash consisting of small, red and inflamed lesions or lumps is the main sign and symptom of actinic prurigo.  The rash often appears hours or days following sun exposure.

Although said to resemble eczema (atopic dermatitis), actinic prurigo results in rashes that typically affect sun-exposed areas, including the following:

• Face (nose, forehead, cheeks, chin and earlobes)
• Neck 
• Chest 
• Extremities (legs, arms, hands or feet) 
• Lips (60-70% of cases)
• Eyelids and the lining of the outer eye (45% of cases) 

Patients with severe actinic prurigo, although less common, may also develop: 

• Rashes in sun-covered areas, including the buttocks 
• Scarring 
• Skin thickening 
• Excoriations (skin picking) 
• Hypo- or hyper-pigmentation (lightening or darkening of certain skin areas, respectively)
• AP cheilitis (dry, scaly lip lesions which, if left untreated, can result in skin cancer)
• Conjunctival disease (red, inflamed eyes) 

Management and treatment for actinic prurigo

Currently, there is no cure and is best treated with several management techniques.

Management for actinic prurigo

Since actinic prurigo worsens mainly during the warmer summer months, the main and most efficient way to manage actinic prurigo is by limiting and avoiding both UV light and sunlight exposure. You can achieve this by adhering to sun protection strategies, including:

• Wearing UV light-protective sunglasses, clothes that cover the extremities and a hat that covers the face, neck and ears. 
• Sitting in the shade during high sunlight hours 
• Regularly applying sunscreen with a sun protection factor (SPF) higher than 30 or more (to protect against UVB) and suncream with a UVA circle logo/4 or 5 UVA stars (to protect against UVA)
• Applying photoprotective window films to car or house windows

Treatment for actinic prurigo

Treatment involves the use of the following medications or remedies:

• Emollients (or moisturising creams) to help relieve itching
• Topical corticosteroids (or steroid (hormone) creams) to help decrease redness and skin irritation
• Antimalarial drugs to help reduce inflammation due to their anti-inflammatory activity
• Immunosuppressive agents to help decrease the exaggerated immune response that occurs after sun exposure (these should only be used until symptoms improve, then gradually reduced and eventually stopped)

Pregnant people and anyone trying to conceive are advised not to use immunosuppressive agents (such as with thalidomide) as it can cause peripheral neuropathy (severe nerve damage to the hands, feet and arms) and teratogenicity (birth deformities).¹

FAQs

How is actinic prurigo diagnosed?

Actinic prurigo (AP) will usually be diagnosed by a dermatologist who assesses your medical history and performs a physical exam. During the physical exam, the dermatologist will look for visual symptoms, mainly the presence of the ‘’hallmark’’ skin rash on sun-exposed areas.¹

To confirm the diagnosis of actinic prurigo, the dermatologist will ask for the following series of investigations to be performed:

• Blood and urine tests - to rule out and exclude other rare sunlight-induced diseases, including lupus erythematosus and porphyria
• Skin photo-testing - to see how the patient reacts to UV light and visible light 
• Genetic screening - to check for the presence of the HLA-DR4 allele variant 

How can I prevent actinic prurigo?

If you have the gene allele for actinic prurigo, it is unlikely that you will be able to prevent the condition. Currently, more needs to be understood about the cause and developmental process of the disease before any preventative treatment can be implemented. 

An active case of actinic prurigo can, however, be prevented from worsening as symptom severity can be reduced by following sun protection strategies.

Who is at risk of actinic prurigo?

Aside from people who carry the disease subtype of the HLA-DR4 allele,¹ the following are more at risk of actinic prurigo: ^1,2 

• Children assigned-female-at-birth (AFAB) - actinic prurigo affects twice as many AFAB children than children assigned-male-at-birth (AMAB)  and usually those between 6-8 years old. 
• People with darker skin types, such as those of Latin or Native American descent 
• People living in dry, warm climates with altitudes higher than 1000 metres above sea level
• People who have been exposed previously to environmental antigens (irritants that invoke an immune response and antibody production) such as wood smoke
• People living with domestic pets or working with farm animals. 
• People who have a family history of actinic prurigo (often termed “familial actinic prurigo’’) 

How common is actinic prurigo?

Actinic prurigo (AP) is very rare, only affecting around 1 in 1000 people worldwide. AP rarely affects people in Europe and Asia, while approximately 60-80% of the people who report having a genetic disposition to AP are of Mexican descent.² 

When should I see a doctor?

See your doctor, general practitioner (GP) or other healthcare providers if:

• Any of the signs and symptoms persist and worsen over time 
• You are pregnant or trying to conceive and are considering starting thalidomide treatment 
• You suspect you have a genetic disposition to actinic prurigo and want to receive a diagnosis and treatment for your symptoms.¹

Summary

Actinic prurigo is a rare skin disease that is caused by exposure to both UVA and UVB rays from sunlight. It typically runs in families (familial actinic prurigo) and worsens during the early spring and summer months. Upon sun exposure, actinic prurigo causes an exaggerated or allergic immune response. Therefore, it is believed that actinic prurigo might be a genetically driven autoimmune disease as the immune system is strongly involved and affected. Signs and symptoms of actinic prurigo involve a rash consisting of lesions mainly in sun-exposed areas, extreme itchiness and painful inflammation. In severe cases, actinic prurigo may also result in AP cheilitis, which can develop into skin cancer if left untreated and/or conjunctival disease. You should receive a diagnosis from your doctor once you’ve undergone any one of the genetic screening or skin tests, and management of the disease will mainly consist of protecting your skin from UV rays and sunlight. You may also be prescribed oral or topical drugs depending on your GP’s advice to help manage your symptoms. You should always follow your doctor's advice when taking any new medications, especially when pregnant or in the process of conceiving and you should make a follow-up GP appointment if your symptoms worsen or your condition becomes too difficult to manage at home.