Medicines and the sun: who gets burnt without knowing it

In summer, advice about the sun almost always arrives late: it is given when the patient walks in with a red back. The useful moment was three days earlier, when they picked up their antibiotic, knee gel, or blood pressure tablet, and no one told them that they needed to cover up more than usual that summer.

Phototoxicity and photoallergy are not the same, and the advice changes

Both are put in the same drawer—"photosensitivity"—and handled the same way, but they behave differently, and that changes what you need to say at the counter.

The practical consequence: in a phototoxic reaction, you can negotiate with the sun—less exposure, more protection, sleeves—because it depends on the amount. In a photoallergic reaction, there is no safe dose: you must withdraw the product and not use it again, because next time even less is enough.

The drugs that cause the most burns in a Spanish pharmacy

The complete list of medicines with described photosensitivity is very long and useless at the counter. These are the ones actually dispensed in summer:

If you want to check a specific drug—or review all of a patient's medication at once—you have the vademecum and the interaction checker.

Topical ketoprofen deserves a separate mention

It is the most forgotten and causes the worst reactions. A gel for a muscle strain does not seem like a «serious» medicine, so it is applied, you go out into the street and no importance is attached to it. Photoallergic reactions to ketoprofen can be severe, extend beyond the application area and reappear weeks later with a new exposure without having used the product again.

Three things that must always be said, and do not take more than fifteen seconds:

1. 1
   Cover with clothing, not with cream

   Sunscreen does not replace covering it up. The treated area must remain covered with fabric throughout the entire treatment.
2. 2
   Two weeks after finishing

   The drug remains in the skin when there is no gel left in sight. This is the fact that no one expects and the one that prevents relapse.
3. 3
   Wash your hands when applying it

   Otherwise, the reaction appears on the back of the hands, which is the area that receives the most sun and the one that nobody connects to the knee.

Hydrochlorothiazide is not a problem just for this summer

It is different from the rest of the table because the risk is not getting burned one day: it is cumulative. The Spanish regulatory agency AEMPS reported in 2018 an increased risk of non-melanoma skin cancer —basal cell carcinoma and above all squamous cell carcinoma— associated with prolonged use and high cumulative doses of hydrochlorothiazide. The absolute risk is small and in the vast majority of patients does not justify changing a treatment that works.

What does change is the advice: a patient on chronic hydrochlorothiazide must be urged to use photoprotection every year, not just in August, and to check moles or lesions that do not heal. That conversation is one of the kinds that only the pharmacy can have, because it is where that patient shows up every month.

Antihistamines: what people believe and what actually happens

In summer, two almost identical queries come in: «I've come for something for sun allergy» and «does the antihistamine make me burn more?». Both stem from a mistaken idea.

«Sun allergy» is almost never an allergy

What is seen most of the time is a polymorphous light eruption: it appears a few hours after the first strong exposures of the season —the first weekend at the beach, the May bank holiday—, it itches a lot, appears on the cleavage, arms and back of the hands, and spares the face and other areas that have been exposed all year. It usually improves on its own in a few days and fades as the summer progresses.

Since it is not mediated by histamine in the way that urticaria is, the oral antihistamine provides little relief. What actually controls it is strict photoprotection in the first few weeks and gradual re-exposure. Dispensing an antihistamine there is not a serious error, but it is a response that does not resolve the issue, and the patient returns.

It is different with solar urticaria, which is indeed an immediate reaction with wheals within minutes: there the antihistamine does have a role, and the condition warrants evaluation by dermatology.

Second-generation oral antihistamines do not cause relevant photosensitivity

Cetirizine, loratadine, ebastine, bilastine or desloratadine are not among the photosensitising agents to worry about. This can be stated with peace of mind.

Corticosteroids: when they help and when they are a stopgap

Topical corticosteroids are not photosensitising, so that fear can be ruled out. Their problems in summer are different.

In mild sunburn, 1% hydrocortisone for two or three days relieves redness and itching. It is worth being honest: the evidence that it shortens the condition or reduces damage is limited, and the effect is primarily symptomatic. What truly helps is cold, abundant hydration —inside and out— and an analgesic if it hurts.

Where not to use it. Not over ruptured blisters, not on extensive surfaces, not repeatedly, and with great care on the face and in skin folds. And not as a substitute for an assessment: if there are large blisters, fever, chills, nausea or the patient is feeling run down, that is a burn that needs a doctor, not cream.

In children, even less margin. The ratio between body surface area and weight means they absorb proportionally more, so a topical corticosteroid in a child must be used with an indication, at the minimum potency, on the smallest possible surface area and for the shortest possible time. On a child's face, never on the initiative of the pharmacy counter.

Chronic use of topical corticosteroids —the patient with dermatitis who has used them for years— thins the skin and leaves it more vulnerable to the sun and trauma. It is not photosensitivity, but the result looks quite similar.

The sunscreen that actually protects

The large number on the container is the figure that varies least between brands and the one that is looked at most. What truly makes the difference is something else.

La cantidad es el problema, no el número

El factor de protección se mide en laboratorio aplicando 2 miligramos por centímetro cuadrado de piel. Llevado al cuerpo de un adulto son unos 30-36 ml: seis cucharaditas de café, o dos tiras de crema del largo de dos dedos por cada zona grande. En la práctica la gente se aplica entre la cuarta parte y la mitad de eso.

Y aquí está el detalle que casi nadie explica: la protección no baja de forma proporcional. Aplicar la mitad de cantidad de un SPF 50 no deja un 25; deja bastante menos. Por eso un SPF 50 mal aplicado protege peor que un SPF 30 bien aplicado, y por eso el mejor consejo del mostrador no es subir de número, es subir de cantidad.

Un reparto orientativo para un adulto, media cucharadita por zona: cara y cuello · cada brazo · cada pierna (una entera) · pecho y abdomen · espalda.

Lo que hay que mirar en la etiqueta

• El sello UVA en un círculo. Garantiza que la protección UVA es al menos un tercio del SPF declarado. Sin él, el envase sólo te dice lo que protege frente a UVB, que es la radiación de la quemadura, no la del envejecimiento y buena parte del daño acumulado.
• «Resistente al agua» significa que conserva al menos la mitad del factor tras dos baños de 20 minutos; «muy resistente al agua», tras cuatro. No significa que aguante toda la mañana, ni que sobreviva a secarse con la toalla.
• «Pantalla total» y «protección 100%» no existen y no pueden figurar en un envase europeo. El máximo etiquetable es 50+.
• La caducidad y el PAO. El bote del año pasado, medio vacío y con seis meses en el maletero a 50 grados, no es el producto que se ensayó. Si te interesa el detalle, lo contamos en por qué tu crema no lleva fecha de caducidad, y en la herramienta de caducidades se puede descifrar el lote.

Cuándo se aplica

Veinte o treinta minutos antes de salir, sobre piel seca, y se repite cada dos horas, después de cada baño, después de sudar y después de secarse. Las zonas que siempre se olvidan son las mismas: orejas, empeines, nuca, labios —con stick, la crema se come— y la raya del pelo.

Fotoprotección infantil: donde de verdad se juega algo

Si sólo hubiera tiempo para un consejo de todo el artículo, sería este. Las quemaduras solares en la infancia y la adolescencia son uno de los factores de riesgo más consistentes de melanoma en la edad adulta. Lo que se hace con la piel de un niño de cinco años se cobra treinta años después. No hay muchas cosas en el mostrador con ese recorrido.

Y hay una razón biológica: la piel del niño tiene el estrato córneo más fino, menos melanina de defensa y una relación superficie/peso mucho mayor que la del adulto, así que absorbe proporcionalmente más de todo lo que se le ponga encima.

Por edades

Cuánta crema le toca a un niño

La misma regla que en el adulto, ajustada al tamaño. De forma orientativa, un niño de 4 a 6 años necesita alrededor de la mitad que un adulto —unas tres cucharaditas para el cuerpo entero— y uno de 10 a 12 años se acerca ya a la cantidad de adulto. Un truco que funciona con los padres: dos dedos llenos de crema —índice y corazón, desde la yema al primer pliegue— por cada zona grande. Es visual, no hace falta medir nada y se acerca bastante.

Las horas

El pico de radiación en España en verano cae alrededor de las 14:00 hora oficial, no a las 12:00: el reloj va dos horas por delante del sol. La franja a evitar con niños es aproximadamente de 12:00 a 17:00. La regla de la sombra sirve sin mirar el reloj: si tu sombra es más corta que tú, busca sombra.

Y hay dos cosas que se olvidan porque no son de piel: los niños regulan peor la temperatura y se deshidratan antes, así que el golpe de calor va en el mismo paquete que la quemadura. Agua con frecuencia sin esperar a que la pidan, y ojo con el niño que deja de sudar, está decaído o vomita.

Medicines and children in the sun

Most classic photosensitisers are for adults, but there are three that appear in paediatrics and adolescence and are worth keeping in mind:

• Doxycycline — used in children over 8 years old and for adolescent acne. Burns with very little exposure.
• Isotretinoin and topical retinoids — acne. As well as photosensitivity, they leave the skin thinner, drier and more irritable.
• Ketoprofen gel — the sports injury of the adolescent who trains outdoors. The worst possible combination.

If you need to adjust the paediatric dose of any medicine, you have the paediatric dose calculator with the exact mL per presentation.

Already burnt: what to do and when to refer

1. 1
   Get out of the sun and cool down

   Cool water or compresses, 10-15 minutes several times. No direct ice on the skin.
2. 2
   Hydrate inside and out

   Drink more than usual — an extensive burn dehydrates — and use unperfumed emollients. Aloe soothes; it does not cure.
3. 3
   Analgesic if it hurts

   Paracetamol or ibuprofen at standard doses, always following the weight-based guidelines in children.
4. 4
   Do not pop blisters

   They are the barrier. If they break on their own, gentle cleansing and cover. No home remedies: no toothpaste, no vinegar, no butter.

The twenty-second advice

No speech is needed. When dispensing any of the medicines in the table, three sentences:

That is all. And you say it on the day the box is collected, not the day they return red.

Frequently asked questions

Sources

• AEMPS (Spanish agency) — safety information and pharmacovigilance notices.
• CIMA (Spanish agency) — summaries of product characteristics: the cutaneous adverse reactions section for each medicine.
• En Familia (AEP) — children's sun protection recommendations from the Spanish Association of Paediatrics.
• AEDV — Spanish Academy of Dermatology and Venereology.
• AEMET — ultraviolet radiation index forecasts.