• Idiopathic photodermatosis mediated by delayed hypersensitivity to UV-induced cutaneous neoantigens.
• Relative failure of the UV-induced immunosuppression (migration and tolerance of Langerhans cells), with persistence of epidermal Langerhans cells after UVB in EPL; increase in dermal CD11b+ cells; alterations in mediators (IL-10, IL-36, antimicrobial peptides such as LL-37).
• action spectrum: UVB and/or UVA; in many patients it responds to repeated UVA and/or UVB irradiations (positive photoprovocation), occasionally visible.
• Low penetrance genetics; there is no specific HLA as in actinic prurigo.

Elementary injury: pruritic papules (most common), papules and vesicles; erythematous-edematous plaques; micropapular variant (pinpoint).

Distribution: Intermittent photoexposed areas: anterior surface of forearms, back of hands, "V" of the décolletage, upper part of the trunk; with relative poca facial involvement (chronic hardening phenomenon).

PrototypeIntense itching hours-days after the first intense exposures of the year; non-scarring lesions that resolve in 2-10 days if further exposure is avoided.

Findings: Erythema, monomorphic papules per patient (polymorphic between patients), occasional edema.

EvolutionAnnual outbreaks, attenuation with seasonal “hardening”; long-term improvement trend in ~3/4 of patients.

Atypical/variant presentations:

• EPL sine eruption (itching without obvious lesions).
• Micropapular variant (“pinpoint papular”).
• “Summer and spring elbow eruption” (pruritic papules on elbows, adolescents).
• Juvenile spring eruption (vesicles on earlobes, children/young men).

• Photosensitive cutaneous lupus (SCLE, lupus tumidus);
• Actinic prurigo (perennial course, cheilitis/ocular)
• Solar urticaria (immediate onset, ephemeral hives);
• Photoallergic/phototoxic dermatitis (drugs/topicals);
• Cutaneous porphyrias (PCT, VP): fragility, blisters, hypertrichosis;
• Hydroa vacciniforme (childhood, vesicles/necrosis with scarring);
• Chronic actinic eczema, toxic UV erythema, insect bites.

BossSpongiotic dermatitis with papillary dermal edema and perivascular lymphocytic infiltrate superficial-deep (± peri-adnexal); without vasculitis.

FindingsVariable spongiosis, exocytosis; occasional intraepidermal vesicles; mild basal vacuolar degeneration; scattered eosinophils and neutrophils in early lesions.

Immunopathology: IFD negative (Useful for excluding lupus). Investigational IHC/immunophenotype: relative increase in CD11b+ in the dermis

molecular testsNot routinely indicated.

• Cutaneous lupus (band test +, mucin, prominent interface dermatitis);
• Photoallergic dermatitis (eosinophil-marked spongiosis, contact/photopatch history +);
• Actinic prurigo (denser infiltrate, epidermal/nodular hyperplasia, clinical cheilitis/conjunctivitis);
• Hydroa vacciniforme (keratinocytic necrosis, scar);
• Arthropod bite (dense eosinophilia, centro punctum).

Basic phototest (optional): MED UVB/UVA when available for safety and planning.

Photoprovocation (if diagnosis uncertain): Repeat irradiations 3–5 days with UVA (30–50 J/cm²) and UVB (0.75–1.5 MED) over usual exposed area; positive in 50–80%.

Discard differentials according to clinical findings: ANA/ENA (lupus), porphyrins (plasma/urine/feces) if blisters/fragility, photo-patch if you suspect a photoallergy to filters or other substances.

Biopsy:

• Type: Punch 4–5 mm lesion early (<48 h), including epidermis-mid dermis (± subcutis if plaques are present).
• SiteThe most representative and sun-exposed area; avoid highly chronic skin. Discontinue topical steroids for >1 week if possible.
• Contraindications: Relative (uncontrolled anticoagulation, active infection).
• Fixation and samples: 1 bottle in 10% formalin for H&E; if you want to exclude lupusSecond cylinder in physiological saline for IFD (coordinate with laboratory for immediate collection). Label with post-UV time.

First line (acute outbreaks and general measures)

• PhotoprotectionBroad spectrum UVA / UVB, SPF 50+, reapply; dense clothing, hat; avoid peak sun.
• Topical corticosteroid Class II–III 1–2 weeks depending on location; antihistamines for pruritus.
• Short oral prednisolone (25 mg/day for 4–5 days) in an intense outbreak or as a specific “rescue” measure.

Seasonal prophylaxis (“pre-season hardening”)

• NB-UVB phototherapy (311–313 nm) o PUVA 2–3 times/week for 4–6 weeks in early spring (prefer NB-UVB for safety). Maintain regular exposure to preserve hardening.
• Hydroxychloroquine (HCQ) 200 mg every 12–24 h, start 2–4 weeks before season/travel and during months of greatest exposure; evidence of preventive/moderate efficacy.
• High UVA/UVB sunscreens: some trials show complete prevention under experimental irradiation.

Second/third line (selected refractory cases)

• PUVA if NB-UVB fails or triggers EPL;
• Azathioprine/cyclosporine: exceptional use in severe disease (limited evidence, cases);
• Oral nicotinamide (2–3 g/d) or extract of Polypodium leucotomos (≈240–480 mg/d) as adjuvants: heterogeneous data; consider if well tolerated.

Security and monitoring (key pearls)

• HCQ: dose ≤ 5mg/kg/day (actual weight); baseline and annual ophthalmological examination starting at age 5, or earlier if risk factors are present (CKD, high dose, tamoxifen). Advise on ocular safety; compatible during pregnancy if benefit outweighs risk. Monitor for interactions and skin reactions (rare exacerbation of psoriasis).
• PhototherapyErythema/burn, pruritus; PUVA increases carcinogenic risk/cataracts (eye protection). Avoid in patients with a long history of non-melanoma skin cancer or active drug photosensitivity.
• Systemic corticosteroids: reserve for short courses; monitor for hyperglycemia, hypertension, insomnia, and reactivation of infection.
• Nicotinamide: prefer moderate doses (≤1 g/day) for tolerability; high doses may cause GI discomfort; hepatotoxicity is rare (monitor if liver disease is present).

Contraindications

• Regarding HCQ: pre-existing retinopathy, dose >5 mg/kg, advanced CKD not monitored, concomitant use of tamoxifen (increases retinal risk).
• PUVAPregnancy (avoid psoralen), history of melanoma, untreated cataracts (if without eye photoprotection).

• Blisters, scarring, skin fragility, hypertrichosis → cutaneous porphyria (making porphyrins).
• Persistent lesions >3–4 weeks, photodistribution with scaling/scarring, alopecia, oral ulcers, severe photosensitivity → cutaneous/systemic lupus (ANA/ENA, DIF).
• Immediate welts after minutes of sun exposure → solar urticaria (provocation test with lamp; treat as urticaria).
• Persistent keratoconjunctivitis/cheilitis → suspect actinic prurigo.

• El latency time (hours-days after UV) and the improves with hardening They guide EPL.
• Relatively expensive resistant due to chronic exposure.
• IFD negative It helps rule out lupus; photoprovocation reproduces the phenotype in ~50–80%.

• Burfield L, et al. Global prevalence and incidence of photodermatoses: a systematic review in the general population. J Eur Acad Dermatol Venereol. 2023. PMID: 36433668 | DOI: 10.1111/jdv.18772
  Summary: Systematic review/meta-analysis of prevalence/incidence of photodermatosis; provides population ranges and biases.
• Rhodes LE, et al. Polymorphic light eruption occurs in 18% of Europeans… J Invest Dermatol. 2010.
  PMID: 19693026 | DOI: 10.1038/jid.2009.250
  Summary: Multicenter survey (n=6,895) estimating EPL prevalence and latitudinal distribution.
• Gruber-Wackernagel A, et al. Long-Term Course of Polymorphic Light Eruption: A Registry Analysis. Front Med (Lausanne). 2021.
  PMID: 34336899 | DOI: 10.3389/fmed.2021.694281
  Summary: Registration cohort with long-term follow-up; describes evolution, time to remission/improvement.
• Lembo S, Raimondo A. Polymorphic Light Eruption: What's New in Pathogenesis and Management. Front Med (Lausanne). 2018.
  PMID: 30250845 | DOI: 10.3389/fmed.2018.00252
  Summary: Updated narrative review of pathophysiology and therapeutics.
• van de Pas CB, et al. Ultraviolet‑radiation‑induced erythema and suppression of contact hypersensitivity in PLE. J Invest Dermatol. 2004.
  PMID: 15009708 | DOI: 10.1046/j.0022-202X.2004.22201.x
  Summary: Experimental study showing suppression of CHS and erythema parameters in EPL vs controls.
• Palmer RA, Friedmann PS. Ultraviolet radiation causes less immunosuppression in PLE than in controls. J Invest Dermatol. 2004.
  PMID: 15009707 | DOI: 10.1046/j.0022-202X.2004.22213.x
  Summary: Human trial demonstrating relative resistance to UV-induced immunosuppression in EPL.
• Wackernagel A, et al. Langerhans cell resistance, CD11b+ influx… after UV exposure in PLE. J Invest Dermatol.2004.
  PMID: 15140244 | DOI: 10.1111/j.0022-202X.2004.22506.x
  Summary: Post-UV immunohistochemical findings in EPL vs healthy skin (LC/innate response).
• Kölgen W, et al. Differential expression of cytokines in UV-B-exposed skin of PLE patients. Arch Dermatol. 2004.
  PMID: 15023773 | DOI: 10.1001/archderm.140.3.295
  Summary: Cytokine profile and LC migration after UVB; suggests defect in immunomodulatory pathways.
• Rossi MT, et al. Cutaneous infiltration of plasmacytoid dendritic cells and T regulatory cells in PLE. J Eur Acad Dermatol Venereol. 2018.
  PMID: 29430717 | DOI: 10.1111/jdv.14866
  Summary: Immunohistochemistry (BDCA2, FOXP3) in EPL lesions; increased pDC and Tregs.
• Schornagel IJ, et al. Diagnostic phototesting in PLE: optimal number of irradiations. Br J Dermatol. 2005.
  PMID: 16307671 | DOI: 10.1111/j.1365-2133.2005.06954.x
  Summary: Determines the number of exposures for efficient diagnostic photoprovocation.
• Schleyer V, et al. A randomized, double-blind SPF study in PLE: efficacy of different UV filters. Br J Dermatol. 2008.
  PMID: 19002338 | DOI: 10.1111/j.1365-2133.2008.08805.x
  Summary: RCA comparing UVA/UVB photoprotectors in outbreak prevention.
• Murphy GM, et al. A double-blind trial of prophylactic PUVA and UVB in PLE. Br J Dermatol. 1993.
  PMID: 8481544 | DOI: 10.1111/j.1365-2133.1993.tb15319.x
  Summary: RCA comparing PUVA vs UVB as seasonal hardening.
• Murphy GM, et al. A double-blind randomized trial of hydroxychloroquine in PLE. Br J Dermatol. 1987.
  PMID: 3552020 | DOI: 10.1111/j.1365-2133.1987.tb05852.x
  Summary: Double-blind trial; demonstrates seasonal benefit of HCQ.
• Pareek A, et al. Hydroxychloroquine vs chloroquine in PLE: a multicentric comparison. Indian J Dermatol Venereol Leprol. 2008.
  PMID: 18187817 | DOI: 10.4103 / 0378-6323.38401
  Summary: Comparative multicenter study; better profile with HCQ.
• Patel DC, et al. Short-course oral prednisolone in PLE: RCT. Br J Dermatol. 2000.
  PMID: 11069465 | DOI: 10.1046/j.1365-2133.2000.03840.x
  SummaryRescue ACE with prednisolone for 4–5 days; reduces pruritus/lesions.
• Boonstra HE, et al. Polymorphous light eruption: clinical, photobiologic & follow-up study of 110 patients. J Am Acad Dermatol. 2000.
  PMID: 10642673 | DOI: 10.1016/S0190-9622(00)90126-9
  Summary: Large series with spectrum of action and phototherapy results.
• Norris PG, et al. Immunopathological study of evolving PLE lesions. Br J Dermatol. 1989.
  PMID: 2923793 | DOI: 10.1111/j.1365-2133.1989.tb07781.x
  Summary: Post-UV serial biopsies; lymphocyte kinetics (CD4→CD8) without marked epidermal damage.
• de Gálvez MV, et al. Summer and spring elbow rashes is a variant of PLE… Front Med (Lausanne). 2023.
  PMID: 37928475 | DOI: 10.3389/fmed.2023.1260514
  Summary: Prospective series with UVA photoprovocation and biopsy that confirms the “elbows” variant of EPL.