This guide explains how sunlight ages the skin, and the three ways to reduce it: the timing, sunscreen, and shade.
The secret to aging slowly
Most of the visible signs of aging on the face, such as fine lines, wrinkles, dark spots, uneven tone and loss of firmness, are caused mainly by sunlight, not by age alone. The amount of sunlight that reaches the skin can be controlled, which means much of this aging can be slowed.
Sunlight and aging
1Sunlight contains ultraviolet (UV) light, which cannot be seen or felt. Two types of UV light reach the ground:
- UVB causes sunburn. It affects the outer layer of the skin.
- UVA causes most of the skin’s aging. It reaches deeper layers of the skin, where it breaks down collagen and elastic fibres, the structures that keep skin smooth and firm, and it contributes to dark spots.
UV Index measures burning, not aging.
About 95% of the UV light that reaches the ground is UVA. Because UVA does not cause sunburn, its effect is not noticed day to day, but it accumulates over years of ordinary time outdoors.
Protecting the skin from aging therefore means, above all, limiting its exposure to UVA.
Timing
2The strength of the aging light at any given moment depends on three factors:
| Factor | What it is | Its effect |
|---|---|---|
| Location | Where you are on the Earth | Sunlight is stronger closer to the equator and at higher altitude. |
| The sun’s position | How high the sun is in the sky, which changes with the time of day and the time of year | When the sun is high, its light passes through less of the atmosphere and more of it reaches the ground. When it is low, more is filtered out. |
| Cloud | How much cloud is overhead, and how thick it is | Thick cloud reduces the light considerably. Thin or scattered cloud lets most of it through. |
No single factor determines the strength of the aging light. It is the combination of the three: the same time of day can bring strong light in one city and weak light in another, or strong light on a clear day and weak light under heavy cloud. Together, location, the sun’s position and cloud determine when it is best to be outside.
Choosing when to be outdoors is the most effective way to reduce exposure.
- The light is strongest around the middle of the day, roughly from late morning to mid-afternoon in most places, and for longer in summer.
- The light is much weaker in the early morning and late afternoon. Moving outdoor activities, such as walks, exercise and errands, into these hours avoids most of the day’s aging light.
- Aging light lasts longer than burning light. As the sun lowers in the afternoon, the light that causes sunburn decreases quickly, while the light that causes aging decreases more slowly. The risk of sunburn can end well before the exposure to aging light does.
Two conditions are often mistaken for protection:
- Clouds. Light or scattered cloud lets most of the aging light through. A grey or cool day can still bring a high level of aging light. Only thick, dark cloud reduces it substantially.
- Winter. Aging light is lower in winter than in summer, but it remains. The light that causes sunburn falls much more in winter, which is why winter sun seems harmless, while the skin continues to receive aging light.
Sunscreen is the most common form of sun protection, and it reduces the light that reaches the skin. How much it reduces depends on two things: which sunscreen is used, and how it is applied.
SPF measures protection from sunburn. The SPF number shows how well a sunscreen protects against UVB, the light that burns. It does not show how well it protects against UVA, the light that ages. Two sunscreens with the same SPF can protect against aging very differently.
UVA protection is shown separately on the label. The marking depends on the country:
| Region | Label | Meaning |
|---|---|---|
| United States | “Broad spectrum” | Protects against UVA as well as UVB. |
| Europe | “UVA” in a circle | UVA protection is at least one third of the SPF. |
| Japan, Korea and much of Asia | “PA” with plus signs, up to PA++++ | More plus signs indicate more UVA protection. |
Most people apply too little. Sunscreen is tested in a laboratory with a thick layer, much thicker than most people apply. A thinner layer gives much less protection than the number on the bottle. In Aeon’s model, an SPF 30 sunscreen applied in the amount most people use protects against aging light about as much as an SPF of 3. A higher SPF, such as SPF 50, makes up for part of this loss, and in Europe and much of Asia a higher SPF also comes with higher UVA protection.
Timing of application. Applying sunscreen about 15 minutes before going outside allows it to settle into an even layer. Sunscreen wears off with time, sweat and water, so it should be reapplied every two hours outdoors, and after swimming or towelling. It is needed on cloudy days as well as sunny ones.
Mineral and chemical sunscreens. Both types protect the skin when they are labelled for UVA protection. They differ in how they work and how they feel on the skin.
| Mineral | Chemical | |
|---|---|---|
| Active ingredients | Zinc oxide or titanium dioxide | Filters that absorb UV light |
| Strengths | Suits sensitive skin; zinc oxide gives good UVA coverage | Thin and invisible on the skin |
| Limitations | Can leave a white tint, especially on darker skin | UVA coverage varies between filters, so a UVA label is important |
The most effective sunscreen is the one that is applied every day, in the correct amount.
Sunscreen is most effective as a second layer of protection, alongside timing and shade rather than in place of them.
Shade blocks the sun’s direct light, which is the largest share of the light that reaches the skin.
- Wide-brimmed hats shade the face, ears and neck. A brim of at least 7 to 8 cm (about 3 inches) all the way round is recommended. A cap shades only the forehead.
- Umbrellas provide portable shade. In many countries they are commonly carried on sunny days for this purpose.
- Trees, awnings and buildings provide shade along a route. The shaded side of a street receives far less direct light.
- Clothing blocks light. Tightly woven fabrics block more than thin or loose ones. Some clothing carries a UPF rating, which measures a fabric’s protection in the same way SPF measures a sunscreen’s.
Shade does not block all of the light, for two reasons.
Light reflects. Water, the ground, walls and other surfaces reflect sunlight upwards and sideways. Under a hat or umbrella, part of this reflected light still reaches the face from below and from the side. Light-coloured and shiny surfaces reflect more.
Glass lets aging light through. Ordinary window glass blocks most of the light that causes sunburn, but lets most of the light that causes aging pass through. For this reason, sitting by a window does not cause sunburn, while the skin facing the window continues to age. The same applies to the side windows of a car; the front windscreen blocks much more.
For long periods beside a bright window, at a desk or in a car, the exposure can be reduced by moving out of the direct light, using blinds during the brightest hours, or applying UV-blocking film to the glass.
What to do
- Stay out of the strong light. Avoid being outdoors around the middle of the day, when aging light is at its strongest. This applies on cloudy days too, because cloud lets most of it through. The exact hours change with where you are and the time of year.
- Wear sunscreen on your face every morning. Choose one with UVA protection (“broad spectrum”, “UVA” in a circle, or PA++++) and SPF 30 or higher, and wear it on cloudy days and in winter too. Use about a quarter of a teaspoon, put it on 15 minutes before going out, and reapply every two hours while you are outside.
- Stay in the shade when you are out. Wear a wide-brimmed hat, carry an umbrella, or keep to the shaded side of the street. Shade blocks most of the light, but not what water and the ground reflect back up.
Sources
- 1Frédéric Flament and colleagues, Effect of the sun on visible clinical signs of aging in Caucasian skin, Clinical, Cosmetic and Investigational Dermatology, 2013.
- 2World Health Organization and United Nations Environment Programme, Global Solar UV Index: A Practical Guide, 2002.
- 3European Commission Recommendation 2006/647/EC, on sunscreen products and the UVA protection they should give.
- 4American Academy of Dermatology, guidance on choosing and applying sunscreen.
- 5Alfio Parisi and colleagues, measurements of the UV that reaches people in shade and under umbrellas.
- 6Jennifer Gordon and Joaquin Brieva, Unilateral Dermatoheliosis, New England Journal of Medicine, 2012. Cited as a reference; its image is not reproduced.