Photodermatoses: sun-sensitive skin disorders in AU general practice

Photodermatoses are skin disorders caused, triggered, or aggravated by exposure to ultraviolet (UV) or visible light. In Australia — a high-UV continent populated predominantly by fair-skinned individuals — they are especially prevalent. Polymorphic light eruption (PLE) affects an estimated 10–20% of the Australian population and is far the most common photodermatosis seen in general practice. Understanding the spectrum — from the benign and seasonal to the potentially life-threatening — equips the GP to recognise, reassure, manage, and refer appropriately.

A. Core clinical — the AU general-practice framework

Classification

The Australasian College of Dermatologists and eTG photosensitivity module classify photodermatoses into four broad groups:

• Idiopathic/immunological — polymorphic light eruption, actinic prurigo, solar urticaria, chronic actinic dermatitis (CAD), hydroa vacciniforme.
• Metabolic/porphyrias — porphyria cutanea tarda (PCT), erythropoietic protoporphyria (EPP), acute hepatic porphyrias (variegate porphyria, hereditary coproporphyria — with cutaneous features in some).
• Drug-induced — phototoxic (any host, dose-dependent UVA reaction) and photoallergic (Type IV hypersensitivity in sensitised individuals).
• Photo-aggravated — lupus erythematosus, dermatomyositis, atopic dermatitis, rosacea.

History

The single most discriminating question is onset timing after sun exposure (Murphy JEADV 2014):

• Within minutes — wheals, flushing, or circulatory collapse → solar urticaria; immediate burning without visible rash → EPP.
• Hours to days — pruritic papules, vesicles, or plaques → PLE, actinic prurigo, or photoallergic contact dermatitis.
• Days to weeks — blisters, skin fragility, milia, hypertrichosis → PCT.
• Weeks to months persistent — lichenified eczematous plaques on chronically-exposed skin → CAD.

Distribution clue. PLE characteristically involves previously-covered skin — the V-neck area, dorsal forearms, outer upper arms — sparing the chronically-exposed face and dorsal hands (which have “hardened” through repeated low-dose UV). Photo-aggravated dermatoses and drug photosensitivity typically affect the face, neck, and dorsal hands.

Drug history (preceding 8 weeks): doxycycline is the leading phototoxin in Australian general practice — prescribed widely for acne, malaria prophylaxis, Q fever, and remote-area infections. Hydrochlorothiazide-containing antihypertensives — particularly the HCTZ–telmisartan combination, which carries a TGA NMSC safety signal — amiodarone, voriconazole, fluoroquinolones, NSAIDs (piroxicam, ketoprofen gel), and retinoids are other important culprits. Topical photo-sensitisers include fragrances containing bergamot or citrus psoralen oils, topical St John’s Wort, and coal tar.

Systemic features screen: ask about arthralgia, fatigue, mouth ulcers, alopecia, Raynaud’s, and sicca symptoms to exclude underlying lupus or dermatomyositis.

Examination

Distribution mapping is the key clinical manoeuvre. Identify sun-exposed zones (face, V-neck, ears, dorsal forearms, dorsal hands, extensor lower legs) and the spared zones — submental triangle, upper eyelids, post-auricular skin, under the watch strap or collar. A sharp cut-off at the clothing line is essentially diagnostic of a UV-mediated process.

Morphology by condition:

• PLE: symmetric pruritic erythematous papules/plaques/vesicles on previously-covered sites; spares face and dorsal hands; clears over 7–10 days without scarring.
• PCT: subepidermal tense vesicles, skin fragility (blisters from minor trauma), milia, hyperpigmentation, and hypertrichosis (lateral cheeks, periorbital) on dorsa of hands.
• Drug phototoxicity: sunburn-like reaction; may include photo-onycholysis (nail separation with doxycycline or psoralens).
• CAD: lichenified eczematous plaques on chronically-exposed sites; severe cases — leonine facies in older men.

Investigations

First-line workup for any new photodermatosis:

• FBC, LFT, UEC — baseline, and pre-PCT screen (elevated GGT/ALT/ferritin supports PCT; cytopaenias in lupus).
• ANA + ENA (anti-Ro/SSA, anti-La/SSB, anti-Sm, anti-RNP, anti-dsDNA) — mandatory if the photodermatosis is atypical, persistent, associated with systemic features, or could be subacute cutaneous lupus erythematosus (SCLE).
• Vitamin D 25(OH)D — high pretest probability of deficiency given sun avoidance; replete to ≥50 nmol/L.
• Iron studies + ferritin — pre-PCT workup; iron overload (ferritin >300 µg/L male, >200 µg/L female with elevated transferrin saturation) supports PCT and prompts HFE genotyping.
• HCV and HIV serology — mandatory in any suspected PCT (HCV is the single strongest triggering association in Australia).

If PCT is clinically suspected: refer urgently to the Australian Porphyria Centre (RPA Sydney) or equivalent specialist lab for plasma fluorescence emission scan (characteristic 619 nm peak = PCT), urine total porphyrins on a fresh dark-protected sample (uroporphyrin > coproporphyrin ratio), and faecal porphyrin profile.

Management — photoprotection first

Cancer Council Australia and eTG identify photoprotection as the cornerstone of every photodermatosis:

• Broad-spectrum SPF 50+ sunscreen meeting AS/NZS 4399:2017: apply at 2 mg/cm² (~one teaspoon to face and neck; ~35 mL whole body) approximately 30 minutes before exposure, reapply every 2 hours and after swimming or sweating (Schalka Dermatol Ther 2020).
• UPF 50+ clothing, broad-brimmed hat, UV-blocking wraparound sunglasses.
• Peak-UV avoidance (10:00–15:00 across most of Australia; year-round in the tropics) — the SunSmart app provides daily UV index by location.
• Mineral sunscreen (zinc oxide/titanium dioxide) is preferred in patients with a history of photoallergic contact dermatitis, infants, PCT, and EPP.
• Vitamin D supplementation 1000–2000 IU/day is mandatory for any patient on rigorous photoprotection — check 25(OH)D at baseline and at 4–6 months; target ≥50 nmol/L.

B. Idiopathic photodermatoses — PLE, actinic prurigo, and solar urticaria

Polymorphic light eruption

PLE is the most common photodermatosis in Australia, affecting an estimated 10–20% of the fair-skinned population (Fitzpatrick types I–III), with a female predominance (F:M ~3:1) and peak onset at 20–40 years (BAD PLE guideline, Ling Br J Dermatol 2020). The mechanism is a delayed-type hypersensitivity (Type IV) reaction to a UV-induced neoantigen in the skin. “Hardening” through repeated low-dose UV exposure tolerises the skin — explaining why PLE is worst in spring and typically improves by late summer.

Mild-to-moderate PLE:

• Rigorous photoprotection as above.
• Topical mid-potency corticosteroid (mometasone 0.1% ointment) BD for 5–7 days at flare.
• Oral non-sedating antihistamine for pruritus (cetirizine 10 mg daily).
• Gradual spring “hardening” — 5–10 minutes of early-morning low-UV-index sun from August.

Refractory or lifestyle-limiting PLE (BAD Ling 2020; Murphy JEADV 2014):

• Hydroxychloroquine (HCQ) 200–400 mg/day as spring prophylaxis, commencing 2–4 weeks before anticipated high-UV exposure and continuing for 8–12 weeks (off-label; private script ~$15–30 for generic). Per RANZCO hydroxychloroquine retinopathy screening guidelines: baseline ophthalmology at 12 months from commencement, then annually. Confirm dose is <5 mg/kg/day using actual body weight.
• Narrowband UVB (TL-01, 311 nm) hardening course — 3 sessions per week for 4–6 weeks pre-summer at a specialist phototherapy unit; well-supported for reducing PLE frequency and severity (Bilsland Br J Dermatol 1993).
• Specialist-supervised short prednisolone 0.5 mg/kg for 5 days at a severe flare, or as a pre-holiday rescue course — via AMH.

Actinic prurigo

More prevalent in First Nations Australians and Latin-American populations, with HLA-DR4 (DRB1*0407) association. Presents as intensely pruritic excoriated papules and plaques on the face, dorsal hands, and lips (cheilitis). Photoprotection and topical corticosteroid are first-line; thalidomide is most effective for severe cases but requires specialist oversight and mandatory pregnancy prevention (Special Access Scheme, S100 pathway).

Solar urticaria

Rare (<0.5% of urticaria) but potentially life-threatening. IgE-mediated: UV-induced neoantigen → mast-cell degranulation within minutes of exposure → wheals, flushing, and rarely anaphylaxis. Any patient with a history of anaphylaxis on sun exposure requires an adrenaline auto-injector and a documented action plan. Non-sedating H1-antihistamine up to 4× standard dose for mild disease; omalizumab or rush UV desensitisation for severe cases (specialist).

C. Metabolic and drug-induced photodermatoses

Porphyria cutanea tarda (PCT)

PCT is the commonest porphyria worldwide (incidence ~1:10,000), with 80% sporadic cases arising from hepatic UROD enzyme dysfunction driven by modifiable triggers (Singal Mayo Clin Proc 2019). In Australia, the dominant triggers are alcohol, HCV (the single strongest), HIV, oestrogen (HRT/OCP), iron overload including HFE C282Y heterozygosity, and smoking.

GP-level PCT management:

1. Address every modifiable trigger — complete alcohol cessation; HCV treatment (direct-acting antivirals via gastroenterology or sexual health); HIV treatment; oestrogen withdrawal (switch to progestogen-only or non-hormonal contraception); smoking cessation; dietary iron reduction.
2. Therapeutic phlebotomy — 450 mL every 1–2 weeks until ferritin is 25–50 µg/L (typically 6–8 sessions), arranged via Australian Red Cross Lifeblood or hospital outpatient. Monitor FBC, ferritin, LFT, and transferrin saturation monthly during induction.
3. Low-dose HCQ 100 mg twice weekly — alternative or adjunct to phlebotomy (Singal 2019). Critical caution: full-dose HCQ (200–400 mg/day) provokes an acute hepatocellular reaction with fever, transaminase surge, and massive porphyrin release in active PCT — only ever use 100 mg twice weekly for this indication.
4. Annual HCC surveillance (ultrasound + AFP) in PCT patients with cirrhosis or hepatic siderosis, given elevated hepatocellular carcinoma risk.
5. Skin care: gentle handling, mineral sunscreen, gloves for occupational hand trauma.

Erythropoietic protoporphyria (EPP)

Rare (~1:75,000–200,000), presenting in childhood with immediate severe burning and stinging on minimal sun exposure, followed by erythema and oedema on the face and dorsal hands. Afamelanotide (Scenesse) is TGA-registered for adult EPP since 2020 — a subcutaneous α-MSH analogue implant and the only disease-modifying therapy; available through specialist EPP centres at RPA Sydney, Royal Melbourne, and Royal Brisbane. Not PBS-funded at present.

Drug-induced photosensitivity

When drug photosensitivity is suspected: cease or substitute the culprit where clinically possible (e.g., switch doxycycline to minocycline for acne; substitute an ACE inhibitor for an ARB-HCTZ combination). For patients who must continue a photosensitising agent (amiodarone, voriconazole), prescribe rigorous UVA-protective measures including UVA-blocking window film for drivers, as clear glass transmits >60% UVA. Long-term voriconazole users require accelerated NMSC surveillance. Report serious or unexpected drug photosensitivity reactions to TGA DAEN.

D. Australian operations

MBS pathways

• Level C consult (item 36) is appropriate for a new photodermatosis assessment including full sun history, medication review, physical examination, investigations, and photoprotection education.
• Chronic disease management plan (item 721) and team care arrangement (item 723) are appropriate for complex photodermatoses — PCT, EPP, CAD, severe PLE on HCQ — requiring coordination with dermatology, hepatology, ophthalmology, and mental health.
• Mental Health Care Plan (item 2715) for adjustment disorder or depression secondary to lifestyle restriction, particularly in CAD and EPP where there is no curative therapy.
• Telehealth (items 91790/91891) is appropriate for routine follow-up, results review, photoprotection counselling, and HCQ ophthalmology coordination under the 12-month existing-relationship rule. New assessments of suspected SCLE, xeroderma pigmentosum, or severe photo-reactions require face-to-face consultation.

PBS items

• Hydroxychloroquine — PBS-listed for SLE and rheumatoid arthritis; PLE is off-label (private script).
• Prednisolone — PBS general; appropriate for a short-course at severe PLE flare.
• Azathioprine — PBS authority for autoimmune dermatoses (CAD, actinic prurigo); requires TPMT testing before commencement.
• Afamelanotide — TGA-registered for adult EPP; not PBS-funded.
• Therapeutic phlebotomy for PCT: usually no out-of-pocket cost via Australian Red Cross Lifeblood.

Nicotinamide as a chemoprevention adjunct

The ONTRAC trial (Chen NEJM 2015) demonstrated that nicotinamide 500 mg twice daily reduced new NMSC by 23% in high-risk patients via DNA-repair enhancement. This is a reasonable OTC adjunct (~$10–15/month) in patients with chronic photodermatoses at elevated skin cancer risk — particularly CAD, voriconazole users, and organ transplant recipients — but is not a substitute for photoprotection.

E. Special populations

Pregnant patients. Most systemic photodermatosis therapies require specialist input in pregnancy. HCQ is Category C — specialist review before continuation. Thalidomide (actinic prurigo) is absolutely contraindicated. Photoprotection and behavioural modification remain safe throughout pregnancy.

Children. Any child presenting with new photosensitivity, blistering, or freckling on sun-exposed skin warrants urgent referral to paediatric dermatology to exclude xeroderma pigmentosum (XP) — an autosomal recessive DNA-repair disorder carrying extreme risk of NMSC and melanoma in childhood.

Aboriginal and Torres Strait Islander peoples. Actinic prurigo is more prevalent in First Nations populations. The MBS item 715 health assessment is a key vehicle for skin surveillance, vitamin D screening, photoprotection counselling, and sun-smart education delivered through Aboriginal Community Controlled Health Organisations.

Outdoor workers. Agriculture, mining, fishing, construction, and emergency-services workers face high cumulative UV exposure. Doxycycline for occupational purposes combined with outdoor UV exposure substantially increases photosensitivity risk. WorkCover-relevant documentation applies when drug photosensitivity arises in an occupational context.

DVA. Service-acquired photodermatosis — for example, doxycycline-related drug photosensitivity during tropical deployment — may be compensable via DVA gold or white card.

When to escalate

Urgently (same day or emergency department):

• Solar urticaria with anaphylaxis — call 000; adrenaline auto-injector; IV antihistamine; continuous monitoring.
• Suspected acute porphyria attack (severe abdominal pain, neuropsychiatric features, dark urine) in a patient with known or suspected porphyria (AIP, HCP, or VP — distinct from PCT which is never acute). Contact the Australian Porphyria Centre on-call service (RPA).
• Any child with new sun-induced blistering or freckling — urgent paediatric dermatology to exclude xeroderma pigmentosum.

Semi-urgently to dermatology or clinical immunology:

• Suspected SCLE (ANA + anti-Ro positive, photo-distributed persistent plaques).
• Photoallergic contact dermatitis (photopatch testing required).
• Solar urticaria without anaphylaxis (phototesting and specialist management plan).
• PCT requiring phlebotomy coordination or hepatological work-up.

Routine dermatology referral:

• PLE refractory to photoprotection and topical corticosteroid (for HCQ initiation or narrowband UVB course).
• CAD, EPP, or actinic prurigo requiring systemic agents or specialist phototherapy.

What this article is and is not

This is general health information based on current Australian general practice guidelines — eTG photosensitivity, AMH, Australasian College of Dermatologists, Cancer Council Australia — and published evidence including the BAD PLE guideline, ONTRAC trial, and Australian Porphyria Centre protocols. It is not personal medical advice and does not create a doctor–patient relationship. Decisions about specific treatment are made with your own GP and treating clinicians.

For AU patient-friendly resources: Cancer Council SunSmart, SunSmart app, HealthDirect — sun protection, Australasian College of Dermatologists photosensitivity A-Z, Australian Porphyria Centre, Lupus Australia.

For skin emergencies or concerning lesions: attend your GP or nearest emergency department.

---

Sources cited

1. Australasian College of Dermatologists — Photosensitivity A-Z
2. Cancer Council Australia — SunSmart / sun protection
3. Therapeutic Guidelines (eTG) — Photosensitivity disorders
4. Australian Medicines Handbook (AMH)
5. TGA — Afamelanotide (Scenesse) registration for adult EPP, 2020
6. TGA — Adverse event notifications (DAEN)
7. Australian Porphyria Centre — Royal Prince Alfred Hospital
8. RANZCO — Hydroxychloroquine retinopathy screening
9. Australian Red Cross Lifeblood — therapeutic phlebotomy
10. SunSmart app
11. HealthDirect — sun protection
12. Ling TC et al. BAD guidelines — polymorphic light eruption (Br J Dermatol 2020)
13. Murphy GM. Diagnosis and management of PLE (J Eur Acad Dermatol Venereol 2014)
14. Bilsland D et al. Narrowband UVB hardening in PLE (Br J Dermatol 1993)
15. Singal AK. Porphyria cutanea tarda — diagnosis and management (Mayo Clin Proc 2019)
16. Schalka S et al. Sunscreen formulations and broad-spectrum coverage (Dermatol Ther 2020)
17. Chen AC et al. ONTRAC — nicotinamide for skin-cancer chemoprevention (NEJM 2015)