Responsible sun exposure

Sunlight is often associated with beauty, health, sexual attraction, and is generally adored. Many people enjoy sunbathing, and most wear minimal clothing to expose large areas of their skin to the sun. Additionally, it’s common to visit tanning salons in the pursuit of increasing one’s attractiveness and self-esteem.
However, knowledge about the potential damage caused by sunlight is limited and often confused.
After all, the sun is perceived as a source of pleasure, and like other “pleasures” such as smoking and alcohol, the harmful effects are only realized after many years, often when the damage is often irreversible.

The solar spectrum

The solar spectrum is composed of electromagnetic energy with a wavelength range extending from 200 to 1800 nanometers (nm). It is made up of 3% ultraviolet (UV) rays, 37% visible rays, and 60% infrared rays.

Some notions on sunlight

The shortest wavelengths reaching the Earth are ultraviolet (UV) radiation, which range from 200 to 400 nm. Wavelengths between 400 and 760 nm make up the entire visible spectrum. Infrared rays, on the other hand, have wavelengths between 760 and 1800 nm.
UV rays are divided into UVC (200-290 nm), UVB (290-320 nm), and UVA (320-400 nm). Ultraviolet light is the most energetic part of the solar spectrum and is therefore the most dangerous for the skin. UVC rays, the most energetic and dangerous, do not reach the Earth’s surface because they are completely absorbed by the gases in the stratosphere.
Many factors determine the irradiance, or the intensity of UV rays reaching the Earth’s surface and, consequently, the skin. These include the time of day, the season, latitude, altitude, and atmospheric conditions.
UVB irradiance is at its highest intensity between 10 a.m. and 2 p.m. solar time (11 a.m. to 3 p.m. daylight saving time).
UVA irradiance remains constant throughout the day. As a result, the amount of UVA can be from 10 to 1000 times greater than UVB on any given day. However, UVA rays are less energetic than UVB. However, UVA rays are less energetic than UVB rays.
UVB rays, which are more energetic, are also known as erythematogenic rays. Sunburn is almost exclusively associated with UVB exposure.
Sunburn can occur even on cloudy days, as 70-80% of UV rays can penetrate through cloud cover. Under these conditions, sunburns are more common because people tend to stay outside for longer periods, assuming the sun’s effect is reduced due to cooler temperatures (infrared rays are filtered by the clouds).
For every 1000 meters of altitude, the intensity of UVB rays increases by about 14%.
White sand reflects up to 25% of UVB rays. Water reflects up to 95% of UVB rays when the sun is directly overhead.
Snow, white surfaces, and shiny metals reflect up to 70% of UV rays.
Therefore, even under an umbrella or in the shade, there can be significant exposure to reflected UV radiation under certain circumstances.
Most summer clothing transmits UV rays. To check this, you can look at the sun through the fabric—if the light passes through, so will the UV rays. Dark colors provide more protection, and if the fabric is wet, it increases the penetration of rays. A dry white cotton T-shirt provides a protection factor between 5 and 9.

UVA damages skin

Previously, UVA rays were thought to be safer than UVB because they are less energetic and less erythemogenic.
For this reason, tanning salons only used lamps with UVA emissions, considering them to be a safer alternative to regular sunbathing. However, recent data refutes the theory that UVA is actually safer.
Not only do the amount of UVA rays reaching the earth’s surface far exceed those of UVB; but UVA rays can also deeply penetrate the dermis, damaging structures such as collagen, elastic fibers and vessels. UVB, on the other hand, penetrates up to the epidermis only.
UVA rays, therefore, also significantly contribute to photoaging, photodermatoses and phototoxicity or photosensitivity responses to certain drugs.

Sunburn

Sunburn is almost exclusively caused by UVB rays. These rays are particularly energetic and penetrate the entire epidermal layer, damaging the structure of keratinocyte cells. This causes keratinocytes to release cytokines, chemical substances that cause: immediate vasodilation (the widening of blood vessels, causing increased blood flow) resulting in erythema; the stimulation of nerve endings, which causes itching, and inflammatory reactions from mainly neutrophil cells. In individuals with fair skin, erythema can occur within just a few minutes of exposure to intense sunlight, accompanied by an itchy, prickly feeling. During prolonged exposure, keratinocyte death occurs due to the destruction of the cell membrane. This results in the considerable release of chemotactic and vasoactive factors, followed by exudation and blistering.
Sunburn can therefore be considered as an acute, toxic phenomenon that mainly affects keratinocyte cells.

Skin light sensitivity (photosensitivity) reactions

When exposed to UV radiation, some chemical or pharmacological substances can cause adverse skin reactions, such as photoallergy and phototoxicity. Table 1 lists the main agents that induce photosensitivity.

Table 1: Example of agents that can induce photosensitivity

Phototoxicity

Phototoxicity is a non-immunological, toxic response to a chemical substance and subsequent light exposure.
The most common phototoxic reaction is similar to a case of severe sunburn (irritation, erythema, pruritus, and edema), yet is unrelated to the duration of UV exposure.
Some allergic reactions can appear immediately, while others may appear hours or days after. Unlike photoallergic reactions, phototoxic reactions are confined to the site of exposure.
For both photoallergy and phototoxicity, reactions can persist for months or years, even after exposure to the chemical substance or solar radiation has ceased.

Photoallergy (sun allergy)

Sun allergy is an immunological response that occurs when a photo allergen (a photosensitizing chemical) absorbs radiant energy and provokes an immune response, which can be in the form of antibody production or sensitized T lymphocyte formation. When next exposed to UV radiation, an allergic reaction will appear, most often in the form of an eczematous response such as erythema, itching and exudation. Vasodilation and edema may also occur. Regardless of the specific symptoms displayed, photoallergy responses can affect any part of the skin, as with solar urticaria.

Skin cancer

Skin carcinogenesis occurs through three distinct mechanisms: initiation, promotion, and conversion into cancer. Initiation develops rapidly, even after a single exposure to a carcinogen like UV radiation. UV initiation damages the DNA by forming pyrimidine dimers, which can lead to changes similar to genetic mutations.
Epidermal cells have a high capacity for repair; however, repeated UV exposure can act as promoters, similar to many chemical or pharmacological substances.
The result is the formation of “premalignant” neoplasms, such as actinic keratosis or squamous papillomas.
In the third stage, premalignant cells are converted into malignant cells; conversion can occur spontaneously or following exposure to mutagens. The skin’s immune system can prevent progression to the conversion stage. Two immune system cells are particularly sensitive to UV radiation: Langerhans cells and T lymphocytes (T4 and T8). Langerhans cells, even with minimal exposure, lose their immune surveillance functions and decrease in number. In chronic UV exposure, suppressor T lymphocytes increase while helper T lymphocytes decrease, although the exact mechanism of these reactions is not yet fully understood.

Skin tumours

Skin cancers induced by exposure to ultraviolet radiation are the most common neoplasms among the Caucasian population.
Approximately 250,000 skin cancers are diagnosed in Italy each year.
The carcinogenic role of UV radiation is universally accepted . Severe photoburn in childhood can increase the risk of skin cancer by as much as 50%.

Basal cell carcinoma

For people with white skin, basal cell carcinoma accounts for about 76% of all skin cancers. The risk of basal cell carcinoma increases with age and, until a few decades ago, this form of cancer was most commonly found in patients aged over 70 or 80 years old. Today, however, basal cell carcinoma is often seen in patients in their thirties and forties, with incidence rising steadily from age 35. As the population ages, it is predicted that more than 70% of people who reach old age within the next twenty to thirty years will develop at least one basal cell carcinoma.

Squamous cell carcinoma

Squamous cell carcinoma is responsible for 20% of skin cancers and is the most common form of skin cancer in people with black skin. Squamous cell carcinoma rapidly develops in areas exposed to UV light and metastasizes to other parts of the body. The most frequently affected area is the lower lip (sailor’s tumor) and cases are often preceded by precancerous lesions (actinic cheilitis). In addition to the lower lip, cases of squamous cell carcinoma on the face and scalp are increasing.

Melanoma

Melanoma accounts for 5% of skin cancer. It causes the anaplastic growth of melanocytes that can rapidly invade other tissue and can quickly lead to patient death. In the last twenty years, cases of melanoma have doubled in incidence and have increased at a faster incidence than other cancerous tumors, with the exception of lung cancer in women and lymphoma linked to HIV. The correlation between melanoma and UV rays is clear, and the risk of tumor increases proportionally with UV exposure. In people who get melanoma, there is often a history of sunburn throughout childhood, so much so that the risk of developing melanoma doubles if someone has been sunburnt five or more times as a child.

Photodermatoses

In many cases, photodermatoses do not have a precise etiology. Instead, photodermatoses are a collection of abnormal reactions to the sun’s UV rays, particularly UVA. Table 2 lists some skin diseases that worsen with exposure to UVA rays.

Table 2: Skin diseases that worsen with exposure to UVA rays

In temperate climates, polymorphic light eruption affects up to 10% of the population. After exposure to light, dermatological reactions include eczematous eruptions, blisters, plaques, papules and extremely itchy skin. These can also be accompanied by headaches, nausea, chills, and fever. Polymorphic light eruption can either continue throughout a patient’s life from childhood, or resolve itself spontaneously. Women are more likely to be affected than men.

Photoaging

Photoaging is a complex of biochemical and histological changes in the skin caused by continuous sun exposure, resulting in a particular type of premature aging. While photoaged skin becomes evident in maturity or old age, UV damage is already present from youth. This is because 70-80% of UV rays have already been absorbed by the age of 21. Photoaging causes symptoms such as skin dryness, scaling, hardening and yellowing, alongside texture changes and wrinkles. Photoaged skin may appear chronically inflamed with irregular pigmentation due to the presence of many benign, pre-malignant, or malignant lesions induced by photo exposure. It is important that photoaging is not confused with the skin’s natural aging process which, in contrast to photoaged skin, will cause the skin to become thinner, smoother and softer. Photoaging is dependent on overall exposure duration and phototype. The latter refers to a scale of six values that determines the skin’s sensitivity to solar exposure, as illustrated in Table 3.

Table 3: Skin phototypes

Photodamage from exposure to artificial UV rays

The popularity of artificial tanning (sunbeds) has become popular in recent years, particularly among young people. With increased sunbed comes an increase in cases of photodermatosis, photoaging and skin cancers. However, many sunbed users are unaware of these risks due to insufficient communication on the potential dangers of UV lamps. In Italy, there is no specific license required to operate UV-lamps, nor are there specific, routine inspections of them.
They are also readily available for private purchase. In the absence of such controls, regulation and education, the increase in UV-induced skin cancers is easily traceable, particularly in younger people. Sunbeds should be completely avoided by: under 18s, over 60s, pregnant women, women taking contraceptives, those with autoimmune diseases, or who have had autoimmune diseases in the past, and people using photoactive drugs during treatment.

Recommendations for sun exposure

The main facts about solar rays are listed in the table below:

• Table 5: Penetration of solar rays
• Ultraviolet rays pass through clouds
• Snow or white surfaces reflect over 80% of UV rays
• UV rays increase with altitude
• Over 50% of UV rays can penetrate umbrellas and parasols
• 95% of UV rays penetrate water

Key recommendations for safer sun exposure

• Table 6: The main recommendations for the public
• Limit exposure time
• Avoid the sun completely between 11am and 3pm
• When other means of photoprotection are unavailable, use natural mineral light reflectors
• Inorganic sunscreens are safer than traditional sunscreen
• Wearing a hat reduces the risk of skin cancers
• Wearing UV-absorbing sunglasses reduces the risk of cataracts
• Wearing clothing prevents photo burns and photoaging
• Cosmetics and scented wipes should not be used during sun exposure
• Tan intensifiers can cause sunburns
• Self-tanning products and beta-carotene do not protect against UV rays
• Plant extracts do not protect against UV rays and can cause sunburn

Proper sun exposure does not solely mean limiting the amount of time spent outdoors.
Exposure of the skin to sunlight certainly induces beneficial physical effects, including the synthesis of vitamin D and the release of cytokines, as well as psychological benefits.
Proper sun exposure involves limiting the exposure time based on factors such as skin type, season, latitude, and time of day.

• Half of UVB rays reach the earth between 11am and 3pm, so avoiding exposure during this period can prevent up to 50% of UVB-induced photodamage.
• Sunscreen is helpful when other means of photoprotection are unavailable. Inorganic sunscreens do not pose risks of sensitization or toxicity through absorption.
• Wearing a wide-brimmed hat reduces irradiation to the head and face, and can prevent UV-induced tumors in these areas.
• Wearing sunglasses with UV-absorbing lenses reduces both ocular damage (cataracts, retinopathy) and damage to the extremely sensitive orbital area.
• Wearing a t-shirt during outdoor excursions or while swimming reduces photodamage to the shoulders and neck, which are high-risk areas for photoaging and UV-induced tumors.
• Cosmetics or perfumes should be avoided before sun exposure, as they may contain photoactive substances that enhance solar ray damage.
• Do not use scented wipes for sweat cleansing and body cleansing during sun exposure.
• Remember that tanning accelerators increase the risk of photoburn and photoaging and skin cancers.
• Remember that self-tanners do not protect against UV rays.
• Beta-carotene, by depositing in the dermis, does not protect the epidermis from UV rays.
• Many plant extracts (such as fig, bergamot, etc.) contain photoactive substances (coumarins) and should not be applied to the skin as DIY tanning agents due to the high risk of photodermatitis.

Means of photoprotection

Photoprotection occurs through several techniques:

1. avoiding exposure to sunlight
2. covering up with protective clothing
3. using chemical agents to absorb solar rays
4. using mineral physical agents to reflect solar rays

Photoprotection should not be considered an one-off event but a lifetime philosophy to adhere to daily.