Sun Damage and SPF: The Most Important Conversation in Skin Care

If there is one conversation I have more than any other at The London Road Clinic, it is this one. The single most effective skin intervention available, more effective than any treatment we offer, more effective than any product on the market, is daily broad-spectrum SPF. It costs less per year than a single clinic appointment. Its effects compound over decades. And most people are still not doing it consistently.

This article is about what UV actually does to skin, what the SPF number on a bottle actually means, how to get it right, and what can be done about damage that has already accumulated.

What UV actually does

Ultraviolet radiation from the sun reaches the skin in two primary wavelengths, each with a different depth of penetration and a different type of damage.

UVB (wavelength 280-315nm) is the shorter, higher-energy wavelength. It penetrates to the epidermis and is the primary driver of acute sunburn. Its intensity varies with the season, time of day and cloud cover.

UVA (wavelength 315-400nm) is the longer wavelength. It penetrates significantly deeper, through the epidermis and into the dermis, and its intensity is far more consistent: present year-round, at similar intensity throughout the day, passing through cloud cover and through glass. UVA is the primary driver of photoageing. It penetrates to the dermis where collagen and elastin live, activates the enzymes that degrade them, generates reactive oxygen species that damage cellular DNA, and stimulates melanocytes to produce excess melanin.

The cumulative nature of UVA damage is its most important characteristic. It is invisible in real time and accumulates over years.

What SPF actually means

SPF stands for Sun Protection Factor and measures protection against UVB only. An SPF 30 product, applied correctly, allows approximately 1/30th of the UVB that would otherwise reach the skin to penetrate. SPF 30 blocks around 97% of UVB. SPF 50 blocks around 98%.

The critical gap in SPF alone: because SPF measures UVB protection only, a product labelled only with an SPF number tells you nothing about UVA protection. A product that is labelled broad-spectrum has been tested to demonstrate UVA protection as well as UVB. Look for the UVA circle logo on European products, or a PA+++ or PA++++ rating on Asian formulations.

Amount matters. The SPF rating is achieved at a defined application quantity of 2mg per square centimetre of skin, roughly half a teaspoon for the face and neck. Most people apply a fraction of this. Under-application produces substantially less protection than the stated SPF.

Reapplication. SPF is not permanent. Reapplication every two hours during active outdoor exposure is the standard recommendation.

Beyond the bottle: getting more from sun protection

Physical barriers. A hat with a brim, protective clothing and seeking shade during peak UV hours (approximately 11am-3pm in the UK in summer) provide complementary protection.

Antioxidants. Topical vitamin C, vitamin E and other antioxidants quench the reactive oxygen species generated by UV before they cause cellular damage. They do not replace SPF, but applied beneath it they extend the benefit. A topical vitamin C serum applied in the morning under SPF is one of the most evidence-supported additions to a preventative skincare routine.

Retinoids. Topical retinoids do not protect against UV, but they address some of the downstream effects of chronic low-level UV exposure.

What existing sun damage looks like

Photoageing manifests across several dimensions simultaneously.

Solar lentigines (age spots, sun spots): flat, well-defined brown marks appearing on the face, backs of hands, shoulders and decolletage.

Diffuse pigmentation and uneven tone: a generally blotchy appearance to the skin, more pronounced across the cheeks.

Fine lines and texture changes: UV degrades both collagen and elastin in the dermis, producing lines, roughness and a generally less resilient surface.

Vascular changes: UV dilates superficial vessels and impairs their tone over time, contributing to background redness and visible capillaries.

Collagen loss: the underlying structural change that drives the loss of firmness and the crisp edge to facial features over time. Discussed in our guide to collagen, elastin and hyaluronic acid.

Addressing existing damage at LRC

Lumecca IPL is the most direct treatment for solar lentigines and generalised sun-induced pigmentation and redness. A course of two to three sessions. Without rigorous ongoing SPF, pigmentation returns.

Chemical peels using glycolic, lactic and blended acid formulations accelerate cell turnover, improve epidermal texture and clarity and help fade diffuse pigmentation.

SkinPen microneedling addresses the collagen component of photoageing, stimulating new dermal collagen and improving skin firmness and texture over a course.

Profhilo addresses the hydration and skin quality component, particularly in skin that looks flat, dull or has lost its surface freshness due to years of UV-driven hyaluronic acid depletion.

In all cases, the most important part of the treatment plan is what happens after the treatment. Treating sun damage without addressing the SPF habit means repeating the same treatment every year.

Frequently asked questions