disclaimer: this information is not intended to provide medical advice, and is only intended for informational purposes. I am not a dermatologist, but I am familiar with cosmetic chemistry behind topical pharmaceuticals, evaluating clinical trials design and data, and making evidence-based recommendations for patients with skin concerns that qualify for self-care treatment and prevention.
I will always start with sunscreen because it is the most important step of skincare - If you only can take away one thing from this guide please let it be the importance of sunscreen and protecting your skin from the sun with protective habits. Don’t even bother wasting your time, energy, and money on skincare if you are not going to protect it from the sun, you’ll just be catching up from a losing battle.
Ultraviolet radiation causes skin cancer, photoaging (hyperpigmentation, sunspots, deep wrinkles, fine lines, skin sagging, etc), and photosensitivity (inflammation, irritation, dryness, redness, tenderness, peeling). Not to mention it suppresses the immune system in the skin, so even if these issues are not concerning to you, please keep in mind that your skin will always prioritize DNA damage over any other conditions (acne, eczema flares, fungal or bacterial infections, trauma from cuts or burns, etc).
Light with a longer wavelength can travel further and has a lower frequency (less energy). Ultraviolet radiation generated by the Sun produces UVA, UVB, and UVC.
UVC has the highest frequency and shortest wavelength so it is completely absorbed by the ozone layer, so you don't need to worry about this unless you have a niche occupational hazard like welding torches or something.
UVB has a short wavelength that reaches the epidermis/top layer of your skin.
UVA has the longest wavelength and can penetrate into the deeper layers of your skin (dermis).
Tanning occurs as the skin's response to DNA damage; so there is never a safe tan (at least not a real one).
Please keep in mind Sun Protection Factor (SPF) only refers to UVB protection;
USA/Australian sunscreens are labeled as "Broad-Spectrum" if they also protect from UVA (it is an all or nothing label), whereas other countries may measure UVA protection separately, like a PA rating where more "+" is more protection.
Tip: Obviously any SPF is better than 0, but an SPF of at least 30 is recommend, and anything above that doesn't do much, right? Well not exactly, because in real life people tend to underapply the amount of sunscreen needed to reach the label protection, so I would personally recommend to wear a higher SPF in hopes that you will get at least an SPF 30 coverage even if you underapply a little! Also make sure it is labeled as broad-spectrum/or has a high PA rating depending on the country of origin.
Sunscreen is just a tool in sun-protection, it is not physical armor! Please take other sun-protective measures: