Sunscreen Application: Ensuring Safety 

1. What is the recommended SPF (Sun Protection Factor) for sunscreens?  

Currently, several medical associations recommend the use of broad-spectrum sunscreens with SPF ratings of 30 or higher. Despite the common misconception that SPF values are multiplicative (for instance, SPF 30 is not twice as effective as SPF 15), there is substantial evidence indicating that higher SPF values are indeed more effective in providing sun protection. 

Recommendation: Studies have consistently demonstrated that the SPF value decreases when sunscreen is inadequately applied. This implies that it is preferable to use a high-SPF sunscreen, such as one exceeding 50, to account for the common practice of insufficient sunscreen application. 

2. What Is the Best Formulation for Sunscreens?  

The formulation of sunscreen plays a crucial role in its effectiveness and user adoption. 

Worldwide, emulsion products such as lotions and cream/gel creams are the most commonly used. These emulsion types can be broadly categorized as either oil in water (O/W) or water in oil (W/O).

Recommendation: Generally, the water-in-oil (W/O) emulsion is the recommended formulation for sunscreens to achieve the highest SPF and water resistance.  

3. What are Water-Resistant Sunscreens? 

Studies found that nearly all the protective effect of non-water-resistant products disappeared after 20 minutes of water immersion. 

Water-resistant sunscreen products are designated as resistant if they maintain their protective properties during 40 minutes for water and 80 minutes for sweat, following moderate activity in indoor fresh water with temperatures ranging from 23°C to 32°C (73°F to 90°F). 

4. What Amount of Sunscreen Should You Use?  

The FDA and international guidelines advise applying 2 mg/cm² of sunscreen, which translates to 35 ml per application to effectively cover the average adult body surface area of 1.73 m². 

However, the average consumer often apply significantly less, typically between 0.5 and 1.5 mg/cm². The key factor in sunscreen application is to use a generous amount. 

Recommendation: It is advisable to apply sunscreen generously to all exposed areas. As a practical guideline for consumers, you can use 2-3 tablespoons (1 tbsp=15 ml) for the body and 1-2 teaspoons (1 tsp=5 ml) for the face and neck. 

Alternatively, cover two fingers with SPF 30+ to adequately cover your face, ears, and neck with sunscreen. 

5. How Often Should You Reapply Sunscreen?   

If you initially apply the recommended amount of sunscreen, it's necessary to reapply it only after activities that could remove the sunscreen layer, like swimming, sweating, or experiencing friction. In the absence of these activities within an 8-hour period, there is no specific evidence to suggest a precise frequency for reapplication. 

Certain researchers have determined that a single application within 8 hours is generally effective, provided that the sunscreen is applied in accordance with the recommended formulation and amount. 

Recommendation: In a daily basis, without risk factors, to reapply sunscreen every 8 hours during the day (sunlight). Otherwise, to reapply to exposed areas 15-30 minutes after sun exposure commences and following intense physical activities that may remove the sunscreen, such as swimming, drying with a towel, or excessive sweating and rubbing. 

Interestingly, it has been observed that SPF 30 sunscreens can accumulate in the skin when applied three times a day, resulting in a higher overall SPF. 

6. How Soon Before Sun Exposure Should You Apply Sunscreen? 

Recommendation: Sunscreen should be generously applied to exposed areas 15 to 30 minutes before sun exposure. Additionally, it's advisable to wait 15-30 minutes after applying sunscreen before entering the water to ensure water resistance.