The natural category worries a great deal about hypothetical risks from filters that have been assessed, and comparatively little about an established risk from ingredients it uses freely. This article is about the second.
What phytophotodermatitis is
It is a reaction produced by the combination of a photosensitising plant compound on the skin and subsequent ultraviolet exposure. The compounds most often responsible are furanocoumarins, sometimes called psoralens, which occur in several plant families including the citrus group and the umbellifers, the family that includes celery, parsnip, hogweed and carrot.
The mechanism is understood. A furanocoumarin absorbs ultraviolet and enters a reactive excited state, from which it can form covalent links with DNA and generate reactive oxygen species. The result clinically is a delayed reaction, typically appearing a day or so after exposure, which can range from redness to painful blistering, and which characteristically leaves hyperpigmentation that can persist for months.
The pattern is often distinctive: streaks, drips or handprints, because the reaction maps where the plant material touched the skin. It is a recognised presentation and it is not rare, particularly in summer.
The severity varies a great deal with how much compound was present, how much ultraviolet followed and the individual. At the mild end it is a patch of redness that fades. At the severe end it produces large tense blisters that are painful and take weeks to settle, and the pigmentation that follows can outlast the reaction by many months. Children are frequently affected because the exposures that cause it, handling plants, spilling a drink, playing outdoors, are ordinary childhood activities.
How cosmetics law treats it
Furocoumarins are restricted under the annexes of the Cosmetic Products Regulation, with a specific and considerably stricter limit for sun protection and tanning products than for cosmetics generally. That distinction tells you exactly how the risk was assessed: the hazard depends on ultraviolet exposure, so a product intended to be worn in the sun was treated as the highest concern case.
Separately, a defined list of fragrance allergens must be identified by name in the ingredient list when present above threshold concentrations, rather than being hidden under the collective term for perfume. Many of those named substances occur naturally in essential oils. The regulation is therefore already recording, in the ingredient list of a natural product, the components it considers most likely to sensitise.
Essential oils are a gentler alternative to synthetic fragrance
- What would have to be true
- That the compounds responsible for sensitisation are absent from, or less prevalent in, essential oils than in synthetic fragrance materials.
- That natural origin corresponds to lower allergenic potential.
- What is established
- A defined list of fragrance allergens must be named on cosmetic ingredient lists above threshold concentrations, and many of those substances occur naturally in essential oils.
- Cosmetics law restricts furocoumarins, with a stricter limit for sun protection and tanning products, on the basis of established photosensitising activity.
- What is not established
- That essential oils are less likely to sensitise than synthetic fragrance materials.
- That natural origin reduces allergenic potential. Some of the substances of greatest concern in fragrance allergy are naturally occurring.
Why sun products are the worst case
Three factors line up badly.
- The product is applied specifically before ultraviolet exposure. That is the exact condition required for a photosensitising compound to act.
- It is applied over a large surface area. Face and body, rather than a small area, so the exposed dose is large.
- It is reapplied. Repeated application over a day, with repeated ultraviolet exposure in between.
No other cosmetic category combines those three. It is the reason the regulation singles out sun protection and tanning products for the stricter furocoumarin limit.
The citrus problem in particular
Citrus oils are widely used because they are pleasant, inexpensive and read as fresh and natural. Their furanocoumarin content varies with the species, the part of the fruit and the extraction method: expressed peel oils generally carry more of this chemistry than distilled fractions, and processes exist to reduce furanocoumarin content, producing oils described as furanocoumarin free or with the relevant compound removed.
A formulator who understands this will use a treated grade in a product intended for sun exposure, or avoid citrus oils in such products altogether, and the compliance limits require it. A person following a recipe on the internet will use whatever is in the cupboard.
A blistering, streaky or unusually pigmented reaction appearing a day or two after sun exposure, particularly after handling plants or applying a scented product, should be seen by a pharmacist or your GP. Phytophotodermatitis is a recognised condition, the pigmentation can persist for months, and there are things a clinician can do. Do not attempt to manage a blistering reaction from a web page.
Sensitisation, which is a separate mechanism
Photosensitivity and allergic contact sensitisation are different processes and both are relevant here. Sensitisation is an immune response: a first exposure produces no visible reaction but primes the immune system, and later exposures produce dermatitis. It is dose related, it is more likely with repeated exposure over large areas, and once established it is generally permanent.
Sun products maximise the conditions for it: large area, repeated application, over years, often starting in childhood. Essential oil components that appear on the fragrance allergen list are exactly the substances for which that pattern of exposure carries the most risk.
This is not an argument that scented natural sunscreen causes widespread harm, and no such claim is made here. It is the observation that the risk exists, is established, is recognised in law, and is the opposite of the way the category presents essential oils.
Photosensitivity that has nothing to do with cosmetics
One clarification matters, because the subject is easily confused. Several medicines increase sensitivity to sunlight, including some antibiotics, some diuretics, some anti inflammatory drugs and some treatments used in dermatology. Certain medical conditions do the same. Those are drug induced and disease related photosensitivity, they are entirely separate from a reaction to a plant compound applied to skin, and they are managed clinically.
The reason to mention them here is that a person who reacts badly in the sun may reasonably wonder which of these is happening, and it is not a question to settle from a website. A pharmacist can check whether a medicine you are taking carries a photosensitivity caution, and a GP can look at a reaction. Both are quick, free at the point of use and much more reliable than working through ingredient lists on your own.
What can be said generally is that if you are photosensitive for any reason, the interaction with a fragranced product becomes more consequential rather than less, and the argument for an unscented product is correspondingly stronger.
What follows
For a formulator, that a product intended for sun exposure is the wrong place for expressed citrus oils, for umbellifer derived materials without a phototoxicity assessment, and for high levels of fragrance in general. For a reader, that fragrance in a sun product is a comfort feature rather than a benefit, and that ingredient lists name fragrance allergens for a reason.
And for the category, that a marketing position built on avoiding hypothetical risk while embracing an established one is difficult to defend, and easy to correct. Unscented is available, it is not a compromise, and the argument for it is much stronger than the argument for most of what this category promotes.