Generality
A sunscreen consists of any substance (or material) that can prevent the harmful effects of sunlight on the skin.
UV and SPF rays
Solar radiation
Solar radiations are classified according to their characteristic wavelength. In addition to visible light (perceived by the human eye), infrared (IR) and ultraviolet (UV) rays are distinguished. The latter manage to reach the dermis, producing an effect on the tissues and the metabolic system. Ultraviolet is made up of 3 categories of radiation: UVA, UVB and UVC.
- UVA rays penetrate deep into the skin, promote the release of melanin from melanocytes and a tan. UVAs represent a subtle threat to our skin: they are also present on days with overcast and cloudy skies and, unlike sunburn caused by UVB, do not create particular discomfort immediately; nevertheless, their negative impact can occur even after years. The effect of UVA is reduced by the use of sunglasses and is hampered by protective clothing and sunscreens.
- UVB rays are potentially more harmful and carcinogenic than UVA, but they produce a stimulating action on melanin synthesis and activate the metabolism of vitamin D.
- UVC rays are the most dangerous radiations and, fortunately, they are shielded from the ozone layer in the earth's atmosphere (they do not generally reach the ground).
SPF - Sun protection factor
The abbreviation SPF stands for sun protection factor and provides a numerical indication (from 6 to 50+) related to the product's ability to shield or block the sun's rays.
The evaluation of the SPF is calculated by comparing the amount of time needed to produce a scald on the protected skin with a filter and without a filter. However, it is a common mistake to hypothesize that the duration of effectiveness of a sunscreen can be calculated simply by multiplying the SPF with the length of time needed to suffer skin damage without sun protection. Indeed, a number of factors influence the amount of solar radiation reaching a person, including the duration of exposure, the time of day, the geographical position and the weather conditions.
Choice of the SPF
Dermatologists recommend using a sun protection factor of no less than 15 and, generally, a protection factor of 30 is considered the most suitable index for people who work outdoors for long periods of time. Indicatively, in a laboratory environment, a sunscreen with SPF 30 absorbs about 97% of the UVB rays, while the sun protection factor 15 absorbs about 93%. A high index indicates better protection against burns caused by UVB rays (the greater the SPF, the greater the protection from the action of the sun).
When to choose an SPF 50 or 50+?
A "very high" protection is indicated to prevent skin damage to people with a very fair complexion or for those who carry out winter activities at high altitudes.
As far as protection against UVA is concerned, there is not yet a real rating system, but compliance criteria have been implemented for "broad spectrum " products, ie sunscreens that protect the skin simultaneously from UVA rays and UVB. According to the latest recommendations of the European Commission, a solar must contain substances (filters and screens) that allow a good UVB / UVA protection ratio, where UVA protection should correspond to 1/3 of the declared UVB protection.
According to the European Commission, the labeling of sun protection products must be simple, standardized and understandable, to allow consumers to identify and select solar products "generally recognized as safe and effective" and that offer suitable protection against sunburn, aging early skin and skin cancers. In particular, misleading wording such as "sun block" or "total screen" can no longer be used and products with a protection factor of less than 6 or greater than 50+ should no longer exist. Here is the summary table of the SPF values:
| Protection | SPF |
| Low | 6 - 10 |
| Average | 15 - 20 - 25 |
| High | 30 - 50 |
| Very high | 50+ |
How does it work?
How can sunscreen shield your skin from UV rays?
Sunscreens absorb or reflect UV rays. The active ingredients in the so-called "chemical" sunscreens (salicylates, cinnamates, oxybenzone, octylcrylene and others), thanks to their structure, are able to absorb UV light . Currently, some chemical filters are available on the market that allow complete coverage of the ultraviolet spectrum (UVB, short UVA and long UVA). Titanium dioxide and zinc oxide, on the other hand, are inert mineral substances with strong hiding power, which physically reflect sunlight and are therefore among the so-called physical screens . The original formulas of these "physical" sunscreens give the typically white color when applied to the skin (fortunately, the most recent formulations leave no trace and blend with the natural skin tone).
In addition to filters and / or screens, the formulation of the solar product provides for the addition of excipients, which are responsible for determining the following characteristics: consistency, resistance to water and sweating, ease of application, rapid absorption, permanence of produced on the skin and so on.
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Which one to choose?
The solar product that best suits your needs must meet various objective and subjective criteria. From a cosmetic point of view, it must be:
- able to protect against all ultraviolet radiations (UVB, short UVA and long UVA);
- photostable (ie not modified with light);
- safe, non-toxic and non-sensitizing;
- water resistant (or "very water resistant") and sweat resistant;
- easy to apply and pleasant on the skin.
Other factors that can influence the effectiveness of sun protection are:
| Phototype | People with clear Caucasian skin (especially people with freckles and blond or red hair) must be particularly diligent in applying sunscreen (or shielding their skin with clothes and hats). If you have specific concerns about your particular skin type, your dermatologist's advice can help you identify the most appropriate protection factor. |
| Expected duration and time of exposure | Sun exposure should be avoided during the hottest hours of the day, from 10 am to 4 pm, when the intensity of the sun is higher. |
| Location | Altitude : It is estimated that UV radiation increases by 4% for every 1, 000 meters in altitude. Therefore, at higher altitudes, sunscreen should be applied and reapplied more conscientiously. Latitude : the intensity of the sun becomes greater if you approach the equator, so you should also adapt your sun protection strategies. Climatic characteristics: high levels of temperature and humidity trigger greater transpiration, reducing the potential effectiveness of sunscreens. |
| Age | Children and the elderly require a higher protection factor. |
| Presence of any reflective surfaces | Sand, snow, ice and water can reflect up to 80% of UV rays, intensifying exposure (reflected radiation). |
| Conducting outdoor activities | Regardless of direct and conscious exposure to sunlight. |
| Simultaneous intake of drugs or presence of any concomitant diseases | They can increase sensitivity to the sun. |
The following table reflects the general orientation for assessing skin types:
| Phototype | Hair | Complexion | Tanning | Character of the phototype |
| THE | Blond or red | Milky-White | Very light | Extremely sensitive to the sun. Always needs maximum protection. Develops an erythema evident at any unprotected sun exposure. |
| II | Light or dark blond | Chiara | light | Sun-sensitive skin. Tends to burn easily. |
| III | Dark blond or brown | Chiara | Light-medium | Intermediate skin. Can be burned after intensive exposure to the sun. |
| IV | Brown | Olivastra | dark | Very resistant leather. Not very sensitive, it rarely reacts to intensive exposure to the sun. |
| V | Brown | dark | dark | It never reacts to sun exposure. |
| YOU | blacks | Dark or black | dark | It shows no obvious difference in color after exposure to sunlight. |
Recommendations for use
What are the key factors to consider when using sunscreen?
- For outdoor activities, for long periods of time (4 or more hours of sun exposure), choose a sunscreen that offers a sun protection factor (SPF) of 30 or higher.
- Generally, the SPF number only indicates the effectiveness of a sun protection against UVB rays (therefore against sunburn). To protect the skin from both UVB and UVA rays (which cause premature aging of the skin), look for a sun protection that can provide broad spectrum UV protection (UVA / UVB, these indications are often present on the label or on the packaging of the solar product) .
- Shake the container well and distribute the sunscreen generously over all exposed skin. Most adults should use approximately 35 ml of sunscreen to cover the whole body (a quantity equal to a small glass for each application). Applying a thin layer of product could reduce the ability of the sun filter to absorb or reflect UV light. Pay particular attention to sensitive areas such as the nose, ears and feet. Sunscreen should be spread over dry skin 30 minutes before exposure. Reapply the same amount of sunscreen every 2 hours.
- When a product is presented as water resistant it means that it is able to maintain its protective capacity over time. It is advisable to repeat the application of the product after prolonged contact with water, sweat or various surfaces (towels, vegetation or sand).
- However, the overcast sky requires sun protection, as UV light (in particular UVA) is able to penetrate through the clouds. Sun rays can also pass through the glass. As a result, the skin could be exposed to aging risk also due to the action of sunlight coming from a window. For these reasons, some people include sunscreen in their daily cosmetic routine.
- Shade and protective clothing (wide-brimmed headgear, long-sleeved shirts, etc.) are other methods of shielding the skin from UV rays. Many argue that the first line of defense for the skin is to wear clothing made with sun-protected fabrics, with a UV protection factor (the code is UPF, they are made with a special treatment to block the sun's rays). A simple white cotton shirt offers a UPF between 4 and 8, and if wet it provides less protection.
Does sunscreen lose effectiveness over time?
Over time, contact with the external environment can alter the sun filters contained in the product, even if photostable. Incorrect closure of the bottle, infiltration of sand, etc. can change the effectiveness and characteristics of sun protection. For this reason it is important to take into consideration the expiry date or the PAO index shown on the primary container or on the label, and replace the solar product at the end of this period to avoid any risk to the skin. The PAO index indicates the period after opening (in months, example: 6M) within which the open solar product (and cosmetics, in general) can be used safely.
Can I use sunscreen and insect repellent at the same time?
Yes, but the effectiveness of both will be diminished. The suggested strategy is to first apply the sunscreen on dry skin and after 20-30 minutes the repellent. In addition, some combined products are available that protect against sun and insects.
