SPF stands for “Sun Protection Factor” and is the abbreviation for Lichtschutzfaktor (LSF) in German, also known as the sun protection factor. The SPF indicates how much longer you can theoretically stay in the sun with sunscreen without getting sunburned, compared to unprotected skin. The sun protection factor is calculated using the following formula:

SPF × Skin’s natural protection time = theoretical protection duration

For example, if your skin shows the first signs of sunburn after ten minutes without protection, a correctly applied SPF 50 provides up to 500 minutes of protection, according to the calculation. But be careful: This calculation is based on standardized laboratory conditions—in reality, many other factors play a role. And: This calculation focuses on sunburn. Other long-term damage is not taken into account, even though our skin doesn’t forget it. Resulting consequences such as premature skin aging or skin cancer can manifest years later and then become acute. This means: Skin damage can occur even without sunburn.

What sun protection factor do I need: SPF 50 or 30?
The sunprotection factor (SPF) indicates how well a product protects against UVB radiation. The higher the SPF, the greater the level of protection. A distinction is made between different protection categories. The following sun protection factor table shows you how SPF values and UVA protection can be classified.

Both the Daily Defence SPF 30 Fluid and the SPF 50 Fluid from DR. EMI ARPA SKIN fall into the “High Protection” category, meaning they provide high sun protection for the skin. They help prevent UV-related skin damage such as sunburn. A rough guideline for everyday use: Sunscreen with SPF 30 or SPF 50 is always advisable; the SPF depends on the situation and skin type. While products with SPF 100 do exist, they are not common, as even sunscreens with the highest SPF cannot filter out all UV radiation. According to the European Commission, claims such as “100% protection” or “sunblock” are considered misleading and may not be used, as they convey a false sense of security. Sunscreens must also carry clear warnings stating that 100% protection is not possible. These warnings are intended to make it clear to consumers that additional precautions, such as avoiding intense sunlight, are still necessary.

Reapplying Sunscreen = Maintaining Protection, Not Extending It

It is essential that sunscreen be reapplied regularly. The statement “Reapplying sunscreen does not extend the duration of protection” therefore sounds contradictory at first. The duration of protection is determined once and for all by the sun protection factor (SPF) multiplied by the skin’s natural protection. And here’s where it gets interesting: It is not extended by reapplying sunscreen, as this only serves to maintain the protection. Daily sunscreen is worn off or reduced by sweat, water, mechanical friction (e.g., clothing, towels), or incomplete application. Over time, the effective protective effect diminishes, even if the theoretical duration of protection has not yet been reached.

In the EU, sun protection products are classified as cosmetic products and are subject to Regulation (EC) 1223/2009. However, additional requirements apply due to their specific protective function. For example, a standardized SPF test according to ISO 24444:2019 must be carried out to determine the sun protection factor. This is an internationally recognized in-vivo test in which test subjects are used to measure how long it takes for a sunburn to develop on unprotected skin compared to skin treated with sunscreen. The SPF value determined indicates how much longer a person with sunscreen can be exposed to the sun without getting sunburnt.

Our skin has a natural defense mechanism against UV radiation—known as the natural protection time. This refers to how long the skin can be exposed to the sun without additional sun protection before the first signs of UV-related damage, such as redness or sunburn, appear. This duration varies from person to person and depends on skin type. While very fair skin types (Type 1) have only 5–10 minutes of natural protection time, darker skin types (Type 6) can have up to 90 minutes. Skin types are classified according to the so-called Fitzpatrick scale. It helps determine the right sun protection for each skin type—and assists, for example, in deciding whether to opt for sunscreen with SPF 30 or SPF 50. But even though our skin offers a certain degree of natural protection, it is not sufficient—because UV rays penetrate much deeper and are more intense than many people realize. That is why sunscreen products are essential, regardless of skin type. Which sun protection factor is the right one? Regardless of skin phototype and natural protection time, SPF 50 is actually always a good idea. Especially when application method, activity level, or external factors reduce the protective effect in everyday life.

The six Fitzpatrick skin types were introduced in 1975 by the American dermatologist Thomas B. Fitzpatrick to create a practical classification system that would allow for a better assessment of patients’ individual sensitivity to the sun. Originally, this classification was not intended for cosmetic skincare, but rather for medical phototherapy. Fitzpatrick developed a scale based on two observations: the tendency to develop a sunburn within the first 24 hours after sun exposure and the skin’s ability to develop a tan within a week.
Based on this, the classification into six skin phototypes was established:

• Type 1: Very fair skin with lots of freckles. Never tans, but reddens quickly in the sun. 
• Type 2: Fair skin with freckles. Tans very little to moderately, and often gets sunburned.
• Type 3: Fair to light brown skin, rarely with freckles. Tans more quickly than Type 2, but sunburn can still occur. 
• Type 4: Light brown, olive-toned skin that tans quickly in the sun. 
• Type 5: Dark brown skin; sunburn is rare. Redness of the skin following UV exposure is uncommon or barely noticeable. 
• Type 6: Dark skin, very high natural pigmentation, sunburn is very rare, and redness is usually not visible. 
  
  Today, the Fitzpatrick classification is widely used. It serves to assess an individual’s risk of UV-related skin damage and skin cancer, is used to determine the dosage for light and laser treatments, and is also established in clinical studies. Nevertheless, the system is not without controversy, particularly regarding its validity for people with dark skin.
  
  Criticism of the Fitzpatrick Scale
  The Fitzpatrick Scale was originally developed for fair-skinned patients and later expanded to include darker skin types—though without adapting the underlying methodology. A central point of criticism is that the system equates skin color with light sensitivity, even though both can vary independently of one another. Thus, it is entirely possible that darker skin may also react sensitively to UV radiation, for example due to a higher proportion of the less protective pheomelanin. Despite these limitations, the scale has served as a practical tool for many years to enable a rough assessment of sun sensitivity—such as determining which sunscreen with which SPF is the right choice. While people with fair skin (types 1–2) are generally advised to use sunscreen with SPF 50, for more resilient skin types (e.g., type 4) with a lower tendency to burn in everyday situations, an SPF of 30 may also be sufficient. However, it is now known that subjective assessments of skin reactions are not always reliable and that individual perceptions can influence the results. For this reason, it is increasingly recommended to consider light sensitivity and pigmentation separately and not to assess sun protection needs based solely on phototypes. Dark skin can also be damaged by UV radiation, although sunburn is less frequently visible. The risk of DNA damage from UV rays, in the form of premature skin aging and skin cancer, is also present here, albeit lower.
  Therefore, sun protection is important for all skin types, including types 5 and 6.
  
  SUN PROTECTION: THE RIGHT APPLICATION
  For sunscreen to be fully effective, proper application is key. The so-called “3-finger rule” helps with the right amount: three finger-length streaks of sunscreen are recommended for the face, neck, and décolletage. About 30 milliliters are needed for the entire body, which is equivalent to a generously filled palm or, for example, a shot glass. It’s important to apply sunscreen to often-forgotten areas such as the ears, the tops of the feet, the hairline, and the scalp. The cream should be applied 15–30 minutes before sun exposure and reapplied every two hours, as well as after swimming or drying off. Make sure your product offers both a sufficiently high SPF (at least SPF 30) and UVA protection.

A high SPF is important for the skin—but it’s only part of the picture. The sun protection factor (SPF) indicates how long the skin is theoretically protected from sunburn. However, reapplying sunscreen does not extend this protection; rather, it maintains it. The skin’s natural protection time varies from person to person and depends on skin type. But sunscreen is always a good idea, regardless of skin type.
UVB rays are responsible for sunburn, while UVA rays penetrate deeper into the skin and primarily accelerate premature skin aging. A reliable sunscreen must protect against both—with SPF 30 (high protection) or SPF 50 (high protection), depending on skin type and situation. A combination of UVB, UVA, and broad-spectrum filters is therefore essential. Because a good sunscreen is more than just a high SPF: it reliably protects against UVA and UVB radiation, feels good on the skin, and thus becomes a daily companion.
The SPF Fluids from DR. EMI ARPA SKIN combine modern, chemical UV filters for broad-spectrum protection against UVB and UVA radiation, helping to prevent sunburn, photoaging, and long-term skin damage such as skin cancer. What matters is not just the SPF value, but the entire formulation—with lightweight textures, skin-nourishing ingredients, and low irritation potential, making daily use a pleasure.