Hello Dr. Bailey,
You have the BEST information on your website, and I have learned a lot from your blogs. Thanks so much for writing them!
I have recently purchased the Citrix SPF 40 sunscreen. It is the first zinc oxide sunscreen I've found that doesn't turn my face ghost white! I have read about your use of that product.
I have a question on frequency of applying it to my face/neck. Do you think it lasts longer than sunscreens that just rely on chemical reaction on the skin? I put the Citrix product on my face early in morning, and wonder if it has "some" protection even later in the day, albeit probably less protection. I work inside in an office, so during
I am glad you like the Citrix Sunscreen. My family and I have used it for years! It is a really excellent sunscreen - it has protected us well and for that I am deeply grateful to the chemist that created it. Your question about what “rules” apply for reapplication of a mineral zinc oxide sunscreen is a really important one. I want to provide a really thorough answer because sun protection is the number one skin care step for keeping your skin healthy throughout your life.
As your question infers, the need for reapplication depends on the amount of sun exposure. First let's back up and talk about zinc oxide versus chemical sunscreens.
What is the difference between a mineral zinc oxide (physical) sunscreen and a chemical sunscreen?
Mineral zinc oxide sunscreen works by bouncing UV rays off your skin. It bounces almost the full spectrum of UV rays off, which is why I prefer this ingredient to all other sunscreen ingredients, including titanium dioxide.
In the process of bouncing UV rays away from you, some of the zinc oxide particles will eventually be broken down and lost. This loss is nothing compared to the loss of chemical sunscreen molecules, which are designed to be lost as part of their UV protective mechanism. Interestingly, this mechanism of chemical sunscreen action also generates heat as part of the chemical reaction that prevents the ray from entering the skin. Have you ever noticed feeling hotter than expected when wearing chemical sunscreen?
Zinc oxide particle breakdown is slower than chemical UV filter breakdown. It's sort of like you get more “wear and tear" from your zinc oxide product than a chemical product. Just how much we don't know, but it's how the two types of UV filters work.
I like to analogize the concept to 'tennis elbow' the sunscreen eventually suffers from all that bouncing away UV rays that it's doing for you. Thus, when you ask the particles in your zinc oxide sunscreen to bounce off a lot of UV rays, they will break down and you are going to need to put more sunscreen on. This happens when you wear sunscreen in the direct sun for hours at a time without adding additional protective measures to block UV rays.
This 'wear and tear' on your zinc oxide sunscreen by intense UV ray bombardment is why we recommend adding some help for your sunscreen such as using a sun hat, standing in the shade, or remaining indoors for many of those daylight hours. I have great hats and sun umbrellas on my Sun Protection Products page. That sounds like what you are doing! Well done for wearing sunscreen daily even when you expect to be indoors a lot!
So, when sunscreen is used alone for protection of all-day sun exposure, I tell my patients they need to follow the “rules” and reapply even a physical sunscreen with mineral zinc protection every two hours. One easy way is to monitor this is to time reapplication with a rest period such as lunch. Sunscreens also always need to be reapplied after sweating, rubbing, or swimming too.
If, however, a person is in a less intense UV exposure scenario, such as when they are indoors a good portion of the day and/or they are in the shade or wearing a full hat when outside, then the sunscreen’s zinc oxide particles may well last all day. It’s not hard to tell because skin gives us good feedback information. When a sunscreen is not adequately present, skin tans and age spots darken so you know to increase your sun protection measures.
In my life, I have used myself as a handy 'guinea pig' to test sunscreens. My fair Type 2 skin will show a darkening of its age spots if I don’t work really hard to prevent that from happening. On the average day, a good application of zinc oxide sunscreen, being mostly indoors and wearing a hat or being in the shade when outside will entirely prevent my age spots from darkening without needing to reapply sunscreen. If, however, I’m gardening in the sun for hours, wearing a hat, working in the shade when possible but sweating, getting lots of sun (including rays reflected off of pavement or stucco walls), then I need to reapply sunscreen at least midday. If I don't reapply sunscreen then my age spots darken, and my skin may even feel a little sensitive in the evening.
How do you decide if you need to reapply your zinc oxide sunscreen?
Ask yourself these questions:
- How much sunscreen do you initially apply? Is it enough? (I’ve found that the average size face with a full head of hair needs about 1/3 tsp. But this does not include the neck, ears, part line or bald scalp, etc.)
- How high is your sunscreen's SPF? I have the best broad spectrum SPF 50+ zinc oxide sunscreens. Click here to see the products I trust.
- What are your activities for the day? Will you be in the direct sun for hours or will you be mostly inside, or just running a few outdoor errands?
- Are you also applying mineral makeup? It can help to give extra protection.
- Where on the earth will you be and how intense are the UV rays? Are you on the equator or in Norway during the winter?
- Do you sweat a lot and wash off sunscreen in the drips of perspiration, or does your sunscreen stay put once you rub it in?
- How fair and sensitive is your skin to the sun?
- Are you a 'hat person' and have hats handy for times you end up outdoors in the sun unexpectedly?
This is an excellent question. Your skin will tell you if you need to "up" your protection. We just don’t want to learn that lesson the really hard way with a burn or by getting a skin cancer. I tell my patients to watch carefully because a subtle tan is telling them to increase what they are doing for sun protection.
Cynthia Bailey, MD, Dermatologist
Disclaimer: Please realize that availing yourself of the opportunity to submit and receive answers to your questions from Dr. Bailey does not confer a doctor/patient relationship with Dr. Bailey. The information provided by Dr. Bailey is general health information inspired by your question. It should not be a substitute for obtaining medical advice from your physician and is not intended to diagnose or treat any specific medical problem (and is not an extension of the care Dr. Bailey has provided in her office for existing patients of her practice). Never ignore your own doctor’s advice because of something you read here; this information is for general informational purpose only. This post is adapted from an excellent comment that Chuck sent to me in a blog post. I wanted to be certain everyone had a chance to see it because I know that many people share this question.