Sunscreen: How to Choose the Right One and Apply It Correctly
Sunscreen is one of the most essential parts of daily skin care, especially in Thailand, where sunlight is intense all year round. As medical faculty specializing in dermatology, we always stress that applying sunscreen correctly is the most worthwhile investment you can make in protecting your skin. This article explains why sunscreen matters, what SPF and PA mean, the types of sunscreen, and how to choose and use it correctly.
Why sunscreen matters
Sunlight contains UVB rays, which cause sunburn, and UVA rays, which cause skin aging. Applying sunscreen regularly has several benefits:
Skin cancer prevention: Helps reduce the risk of all types of skin cancer
Slower wrinkles: UVA rays are the main cause of wrinkles and premature skin aging
Fewer dark spots: Helps reduce dark spots and discoloration caused by sun exposure
Sunburn prevention: Protects the skin from sunburn caused by UVB rays
What SPF and PA mean
The values on a sunscreen label show the level of protection against each type of ray:
SPF: Sun Protection Factor shows how well the product protects against UVB rays, which cause sunburn. For example, SPF 30 blocks 97% of UVB and SPF 50 blocks 98% of UVB.
PA: Protection Grade of UVA is shown as PA+, PA++, PA+++ or PA++++ and indicates the level of protection against UVA rays, which cause skin aging and are a main cause of skin cancer. The more + signs, the more UVA protection.
Types of sunscreen
Sunscreens fall into 2 main types:
Chemical Sunscreen: Uses chemicals that absorb UV rays and convert them into heat. The texture is light, but some products may cause irritation or allergic reactions.
Physical Sunscreen (Mineral): Uses Zinc Oxide or Titanium Dioxide to reflect UV rays away from the skin. It is generally better suited to sensitive skin and babies.
How to choose sunscreen for your skin type
Sensitive skin: Choose a Physical Sunscreen containing Zinc Oxide or Titanium Dioxide, and avoid Oxybenzone and Octinoxate.
Oily skin: Choose a gel or water-based formula, which helps control oiliness on the skin.
Dry skin: Choose a Moisturizing Sunscreen containing Hyaluronic Acid or Glycerin to add moisture.
How to apply sunscreen correctly
The right amount: Apply enough sunscreen, about 2 milliliters per area (roughly 1/4 teaspoon) for the face and neck.
Apply in advance: Apply about 15-30 minutes before going out in the sun so the sunscreen can work fully.
Reapply: Reapply every 2 hours if you are in the sun or after heavy sweating.
Combine protection: Use it together with physical sun protection such as a hat, sunglasses and long-sleeved clothing.
Frequently asked questions
Is there a big difference between SPF 30 and SPF 50? SPF 30 blocks 97% of UVB and SPF 50 blocks 98% of UVB, so the difference is small. What matters more is applying the right amount and reapplying regularly.
Which type of sunscreen suits sensitive skin? People with sensitive skin should choose a Physical Sunscreen (Mineral) containing Zinc Oxide or Titanium Dioxide, which reflects UV rays, and avoid Oxybenzone and Octinoxate, which may cause irritation.
How much sunscreen should I use, and how often? Use about 2 milliliters per area (roughly 1/4 teaspoon) for the face and neck. Apply 15-30 minutes before going out in the sun, and reapply every 2 hours if you are in the sun or sweating heavily.
What is the difference between PA+ and PA++++? PA shows the level of protection against UVA rays, which cause skin aging. The more + signs (PA+ to PA++++), the more UVA protection, so choose a sunscreen with sufficiently high SPF and PA values.
If you have sensitive skin, melasma or dark spots, or you are unsure which sunscreen suits your skin, you can consult a dermatologist at Siam Dermatology by calling +66 61 448 7000 or through LINE @siamderm for skin care and protection advice suited to you.
Written by Dr. Patara Voravutinon, Dermatologist · Last reviewed 16 July 2026
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