Photoprotection

Who needs photoprotection and how much do they need? A little photoprotection –Healthy population: especially fair skinned people: to prevent sunburning, reduce chronic UV damage and reduce skin cancer risk Absolute and total photoprotection –Xeroderma Pigmentosum a lot of photoprotection –Patients with photosensitive dermatoses –Patients with risk factors for skin cancer:

Photoprotection is not just sunscreen Behaviour: avoiding the sun Shadow (buildings, trees) Clothes and hats Window films Sunscreens

Sunscreen ingredients

Chemical sunscreens: absorbers of UV Octocrylene

Chemical sunscreens: most absorb UVB, a few absorb UVA

Physical sunscreens : ‘ micronising’ titanium dioxide particles UV visible tiny ‘micronised particle: reflects only UV (looks transparent) Normal sized bigger particle: reflects all light (looks white)

Measuring the Photoprotection of a sunscreen UVB: Sun Protection factor SPF = dose to cause sunburn with sunscreen dose to cause sunburn without sunscreen Measured for sunscreen applied at 2mg/cm 2

Measuring the Photoprotection of a sunscreen UVA: no agreed measure Star rating, other ratings: –Either measure protection against UVA effect in the skin, usually ‘persistent pigment darkening’ (ie tanning) –Or use a spectrophotometer to measure how much UVA is taken out by the sunscreen

European Union labelling: UVB protection ‘Low protection’: SPF 6 to 14 ‘Medium protection’: SPF 15 to 29 ‘High protection’: SPF 30 to 50 ‘Very high protection’: SPF 50 +

European Union labelling: UVA protection UVA seal: UVA protection is at least 1/3 of the UV protection

The common sunscreen ingredients

Visible light photoprotection: The ‘Dundee’ sunscreen Needed in visible light photodermatoses: porphyria and solar urticaria

Sun Protective clothing Protection factor of clothing = ‘UPF’

Photoprotection for severe photodermatoses: UV and visible light window filter films

Photoprotection in real life

1) How are sunscreens applied in real life? 2) How do patients and the general population actually behave regarding sun exposure

Sunscreen use varies a lot between different countries

In real life, sunscreen is applied too thinly to achieve the SPF on the label SPF measurement calculation: 2mg/cm 2 Actual application studies: –Children (diaries plus weighing sunscreen tubes): 0.48 mg/cm 2 –Adults (nude beach, single whole body application + weighing tubes before and after): 0.52mg/cm 2 –Adults: (beach holiday, diaries plus daily weighing sunscreen tubes): 0.79 mg/cm 2 –Volunteers (applying sunscreen in a laboratory): 1.00 mg/cm 2

What a SPF50 sunscreen really does 2mg/cm2: SPF 50 (time to burn increased 50 fold) 1mg/cm2: SPF 7 (time to burn increased 7 fold) 0.5mg/cm2: SPF 2.5 (time to burn roughly double)

Patients apply sunscreen especially badly to some places on the body: Photosensitive patients (observed, in a lab)

Real life photoprotection How do you measure sun exposure behaviour?

1) patient diaries 2) objective measures of UV exposure

Wristwatch UV dosimeter

Recent study of 25 Danish holidaymakers on a 1 week holiday in the canary islands: all 25 got sunburnt people used sunscreens to stay out in the sun longer

What about malignant melanoma patients?

At home Days exposing body at home HolidayHoliday abroad Idorn et al., JAMA Dermatol. 2014

Melanoma patients are careful about sun exposure for the first summer only after their diagnosis of melanoma. After that they expose themselves to progressively more sun every summer, and have more UV exposure than matched controls.

Answer to the question: NO