UV, Skin And Oils, Psoriasis And Phototherapy Risks

I sent an email to Health Canada about mineral oil baby oil use on skin and UV and received this back some time ago, colour and bolding added by me. I asked for references too and received them as well. This email information was posted by me online previously but not in this blog. Outside of phototherapy, a lot of oil is not going to do much to protect you from UV without a decent SPF, and a broad spectrum SPF is best. A thicker application of petrolatum (Vaseline), or a cream is about such use negatively affecting desired phototherapy results, and possibly the safety of some types of phototherapy. Risk factors include the number of treatments and the UV dose used. See the end of this post for SPF information in previous blog posts. 

"There are a number of resources that support the fact the baby oil (oils in general) can intensify the absorption of UV rays. First of all, oils applied to the skin causes less reflection and refraction (bouncing-off) of the UV rays, therefore allowing larger proportion of the UV radiation to be absorbed by the skin. The skin surface on close inspection is quite irregular and by applying oils you make the surface smoother and more uniform, allowing a larger proportion of the UV radiation to be captured by the skin. Lastly, there are tiny air pockets between the horny scales in the stratum corneum (the outermost layer of the skin), creating spaces that allow a lot of scattering of the UV radiation. Oil is the perfect substance that is able to seep between these horny scales and minimizes diffusion of UV rays allowing more of it to penetrate deeper into the skin to be absorbed.

Here are a number of resources/references.

Penetration of epidermis by ultraviolet rays. Everett MA, Yeargers E, Sayre RM, Olson RL.
Photochem Photobiol. 1966 Jul;5(7):533-42.

The light barrier of the epidermis Dermatol Wochenschr. 1965 Jul 24;151 (30):887-9.

Increased penetration of epidermis by high intensity ultraviolet rays following the application of vaseline oil.
Leroy D, Dompmartin A, Deschamps P. Photodermatol. 1986 Feb;3(1):51-2.

Change in ultraviolet (UV) transmission following the application of vaseline to non-irradiated and UVB-exposed split skin K. Hoffmann, K. Kaspar, T. Gambichler, P. Altmeyer British Journal of Dermatology
Volume 143, Issue 3, pages 532–538, September 2000"


It is the thickness of the vaseline or petrolatum application, or cream used, which can make a difference in phototherapy. Thicker application of either can result in a higher dose of UV used, or an increased number of phototherapy treatments.

"Effects of topical preparations on the eyrthemogenicity of UVB: implications for psoriasis phototherapy." 1995, colour added by me.
http://www.ncbi.nlm.nih.gov/pubmed/7868718
"Thick application of petrolatum and emollient creams can reduce transmission of UVB. Mineral oil and a clear liquid emollient did not significantly affect transmission or erythemogenicity of UVB."
erythema defined

"Change in ultraviolet (UV) transmission following the application of vaseline to non-irradiated and UVB-exposed split skin." 2000, colour added by me.
http://www.ncbi.nlm.nih.gov/pubmed/10971325
"The thicker the layer of vaseline applied, the lower was the difference in transmission between non-irradiated split skin and UVB-exposed split skin. 
CONCLUSIONS: Application of the correct amount of vaseline can enhance transmission in either the UVA or UVB range, and would enable dose reduction during a course of phototherapy."


While NB-UVB treatment appears to have lower risks, more research needs to be done.

"Incidence of skin cancers in 3867 patients treated with narrow-band ultaviolet B phototherapy", 2008, colour and bolding added by me.
http://www.ncbi.nlm.nih.gov/pubmed/18834483
"CONCLUSION: We found no significant association between NB-UVB treatment and BCC, SCC or melanoma. There was a small increase in BCCs amongst those also treated with PUVA. These reassuring results do not demonstrate the early increase in skin cancers that was found associated with PUVA treatment. However, cautious interpretation is required as the cohort contained relatively few patients who had a high treatment number and because the slow evolution of skin cancers may result in a delayed incidence peak. Ongoing risk assessment is therefore essential."

"Enhanced response of childhood psoriasis to narrow-band UV-B with preirradiation use of mineral oil." 2008, colour added by me.
http://www.ncbi.nlm.nih.gov/pubmed/18950402
"The cumulative dose for clearance was significantly lower on the emollient pretreated side. No adverse effects were observed with mineral oil or narrow-band ultraviolet-B phototherapy. We conclude that preirradiation use of mineral oil enhances the therapeutic efficacy of narrow-band ultraviolet-B phototherapy in children with widespread psoriasis."

Phototherapy risks 2009
"[Narrow-band UVB therapy in psoriasis vulgaris: good practice guideline and recommendations of the French Society of Photodermatology].", colour and bolding added by me.
http://www.ncbi.nlm.nih.gov/pubmed/20110064  
"(2) Adverse effects. The immediate adverse effects were generally of little consequence, with later effects alone posing problems. Because of the risk of induction of cataract, ocular protection must be used during sessions. In the absence of symptoms or known ocular disorder, prior ophthalmologic control is not considered necessary. The risk of skin cancer remains poorly defined, and this risk has not been clearly shown to be lower than with broad-spectrum UVB therapy or PUVA. The studies give no indication of the number of sessions after which therapy must be completely discontinued." 

More and larger studies need to be done. 
"Carcenogenic risks of psoralen UV-A therapy and narrowband UV-B therapy in chronic plaque psoriasis: a systematic literature review." 2012, colour and bolding added by me.
http://www.ncbi.nlm.nih.gov/pubmed/22512677
"CONCLUSION: There is an increased risk of skin cancer following PUVA, shown by both US and European studies. The greater risk measured by the US studies may be at least partly explained by high UVA dose exposure and the lighter phototypes of the treated patients. The lack of prospective studies in psoriasis patients treated with NB-UVB constitutes a barrier to the robust assessment of carcinogenic risk of this phototherapy technique." 

See more about phototherapy at the Mayo Clinic 2015

See Also
The New York Times Article "Phototherapy" 2013, information review date "12/3/2013"
http://health.nytimes.com/health/guides/disease/psoriasis/phototherapy.html
and these blog posts, here, here and here, for more details on SPF and hair and scalp protection.