The sun has beneficial effects on the skin, mainly with regards to well-being as well as Vitamin D synthesis,. The latter is important for bone metabolism (calcium absorption)
How does the sun act on the Skin ?
Of the electromagnetic spectrum Ultraviolet light (UV) is the culprit, and has been studies in depth
There are 3 types of UV:
-UVC: those are normally stopped by the ozone layer, but if they make it to the skin, erythema is induced
-UVB: penetrate the epidermis and are mostly responsible for photoaging, precancers (Actinic Keratosis) and Non-Melanoma Skin Cancers (Basal Cell Carcinoma, Squamous Cell Carcinoma)
-UVA: penetrate deep into the dermis and hypodermis and are responsible for immunosuppression and participate in the development of melanoma.
All the visible light can affect the skin such as in melasma and photodermatoses
Deleterious effects of the sun on the skin
–Photoaging (Clint Eastwood and Sun Damage article)
–Melasma (Chloasma; Pregnancy Mask). Click on the link to read more)
–Solar lentigenes
–Precancerous skin conditions (AK) and cancers (BCC, SCC, Melanoma)
–Photodermatoses
What are photodermatoses ?
Photodermatoses refer to a diverse spectrum of skin disorders that can be caused or aggravated by sun exposure, primarily due to the ultraviolet or visible light component. Broadly, photodermatoses can be classified into 4 categories:
1. Autoimmune photodermatoses (idiopathic): the most common group
–Polymorphic Light Eruption (PMLE)
In Singapore 28% it amounts to 28% of photodermatoses
UVA is its main trigger
It is treated with oral steroids, photherapy desensitization (“hardening”) and sun protection
-Chronic Actinic Dermatitis
Affects older men, in Singapore and amounts to 15% of photdermatoses
UVB is the main trigger
It is treated with oral immunosuppressant therapy, emollients, topical steroids and sun protection
-Actinic Prurigo
Affects mainly the Chinese population in Singapore
Triggers are both UVA and UVB
Treatments consists of topical steroids, oral immunosuppressors and sun protection
-Solar Urticaria
It is quite rare in Singapore
Urticarial lesions occur minutes after exposure and subside in the shade
UVA and visible light are triggers
Treatments consists of photoprotection, oral antihistamines, desentization phototherapy.
2. Drug or chemical-induced photodermatoses
-Phototoxic drug eruptions
They amount to 15% of drug eruptions in Singapore
They are basically clinically equivalent to severe sunburns (blistering)
Triggered by UVA and a long list of incriminated drugs Non-Steroidal Inflammatory Drugs (NSAIDS), ciprofloxacin, amiodarone, statins, diuretics)
Treatment consists of sun protection and topical steroids
-Photocontact dermatitis (Allergic)
The most commonly involved drugs are topical NSAIDS. Also plants sur as lime (phytocontact photodermatitis)
Sunscreens and fragrances are also a cause
-Porphyrias
3. Photoaggravated skin disorders (20%)
Eczema (atopic dermatitis): not that in photaoaggravated Atopic Dermatitis, the phototests is normal
Rosacea: no comedones are present but erythema and telangiectasia can be seen.
Systemic lupus erythematosus: malar rash and photosesitivity
Dermatomyositis
Lichen planus
Bullous pemphigoid
4. Genetic photodermatoses
-Xeroderma Pigmentosum (XP)
caused by a mutation in a DNA repair gene
patients present early with lentigines, photosesitivity, early skin cancers
Treatment consists of strict sunprotection, skin cancer surveillance and multidisciplinary management (as neurological and ocular involvement are present)
How to detect photosensitivity ?
The salient features of the common photododermatoses encountered in the dermatology clinic are as follows
physical examination shows a photodistrubution of lesions (v-neck, hands, and arms…)
How to evaluate a patient with photosensitivity ?
-History (age of onset, duration, exposure, drugs, medical, family history)
-Physical examination (morphology, distribution)
-Investigation (Full Blood Count, Antinuclear Antibodies, phototest, porphyria, photopatch test)
Sun Protection
Sun protection is central to the management of all photodermatoses.
It is important to educate patients on good sun protection measures which include:
The BCS triad (in descending order of importance)
-Behavior
sun avoidance between 10 am and 4 pm
-Clothing: pants, hats, sunglasses, umbrella
Sunscreen:
a high SPF is not enough (to read our articles on SPF, click-here). Counseling recommendation is about 30-50SPF
Apply liberally and broadly
Reapply every 2-3 hours
Tan E – In the Spotlight: Light and the Skin – Common photodermatoses and their Management. Symposium 5 – The Dark Side of Light – Effects of Light on Skin, and Phototprotection. NSC Update in Dermatology and Venereology 2015 – Singapore
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