What is sun protection factor or SPF? How is it defined? SPF is defined as...
the dose of UV radiation required to produce 1 minimal erythema dose (MED) on protected skin after the application of 2 mg/cm2 of produce divided by the UV radiation to produce 1 MED on unprotected skin.
In other words, it's how much of this stuff you need to use to protect your skin from a dose of radiation that would affect unprotected skin. The higher the number, the more protection you should get. (Sort of...see the post below on sunscreens!)
"Water resistant" sun screen must maintain its SPF after immersion in water for 40 minutes. "Very water resistant" sunscreen must maintain its SPF after immersion in water for 80 minutes.
Broad spectrum or full coverage sunscreen will protect against both UVB and UVA rays.
How does SPF work? It's all about you! Let's say you burn after 10 minutes in the sun. SPF 15 will get you 150 minutes in the sun. SPF 30 will get you 300 minutes in the sun. But you have to re-apply after about 2 hours with a non-water resistant sunscreen anyway, so what's the point if you take 20 minutes to burn and you have to re-apply it after about 120 minutes? Because SPF 15 will block out about 93% of the UV rays, and SPF 30 will block out about 97%. For very fair skinned people, going from SPF 30 to 50 might get them another 1% coverage. Might not be a big deal for someone who has dark skin, but if you're like my husband (more below), that 1% could mean the difference between a slight reddening of his skin and a burn.
WHAT EXACTLY IS SUNSCREEN? (Original found here)
There are two types of sunscreen ingredients - physical blockers and chemical blockers. The physical blockers are titanium dioxide and zinc oxide, both of which work by preventing the sun's rays from reaching our skin by reflecting and dispersing them. The chemical sunscreens work by absorbing ultra-violet rays and keep them from penetrating the skin. They are great at blocking about 95% of the UVB rays, but very little UVA. The degree of absorption depends on the type and concentration of chemical sunscreen. Ideally, you'd have a combination of the two in your sunscreen.
To get maximum sunscreen-age, apply it about 15 to 30 minutes before going into the sun so it can penetrate the keratinous layer of your skin. Re-apply it regularly every 2 to 4 hours, and especially if you've been swimming or sweating a lot.
The physical sunscreens are unlikely to cause a reaction on our skin - any reaction you might have is thanks to the other ingredients in the sunscreen - so if you have sensitive skin, stick with zinc oxide and titanium dioxide and be okay with looking a little ghostly (I like this on my face, not so much on my legs!) These sunscreens might feel a little draggy, but it's a small price to pay to avoid sunburns!
If you're out in the sun - meaning, if you ever go outside - don't forget to protect your nose and lips. Your nose gets the most sun exposure, so sunscreen it well. And our lips can be protected with as little as your lipstick on a cloudy day, or with a water resistant sunscreen or lip balm during a sunny day.
Don't forget to get a good pair of UV blocking sunglasses. They'll protect your retinas and they'll make you squint less - and less squinting means fewer wrinkles, so you're looking good as well as feeling good!
So how do we make our own? We don't.
As you may or may not know, my husband has vitiligo, a condition that leaves him without melanin in big patches in his skin and hair. (This is what they say Michael Jackson had, the condition that was making him white. As Raymond is already quite fair skinned, you don't notice it much.) We buy sunscreen by the bucketload in the summer to ensure he isn't at risk for burning, which can happen in a few minutes for him. If I could make sunscreen that I could guarantee would work for him, I'd make it. But there are so many factors that go into ensuring a sunscreen works, I don't feel confident that it will prevent him from agonizing pain today and skin cancer in the future.
If you're considering making your own sunscreen, there is a lot of chemistry to know. (Check out this post from Zenitech!) You have to worry not only about the pH of a sunscreen but the emulsification of our lotion when making a sunscreen. As well, how do you know how effective your chosen sunscreen might be? Only by going into the sun and seeing if it works, and anecdotal evidence is not data - it might have been a cloudier than normal day, you might have been under a tree, you might have really sun resistant skin that doesn't burn for 30 minutes or more! If you have a fair skinned friend, she might burn in 10 minutes, and the product that works well for you might mean sunburn for her!
There are so many scary things out there on the 'net about sunscreen, and I won't give them any validity by putting them into this post. The way I see it? Sunscreens block out the sun's rays. Sun makes me burn. Anything that prevents unnecessary pain today and wrinkling tomorrow works for me. (Click here for a post on pigmented skin through sun exposure and here for a post on photo-aging.)
Yes, I know anecdotes aren't data and this last paragraph is my opinion, but I really haven't found any valid studies showing that sunscreen causes more harm than good.
If you're worried about sunscreens, then don't use them. Or choose sunscreens containing only certain ingredients, but not others. Just choose something...
There is no argument I haven't heard before about why you want to make your own sunscreen, so I'll ask you not to make one. There is absolutely nothing you can say that will make it okay for you to make something that could be quite dangerous to someone. Sunscreen makes my skin break out so badly and my skin is red all summer long because of the irritation, yet I still use it. I have the skill and knowledge to make something that might resemble sunscreen, yet I would not think of doing it, even though it would save my family a ton of money. You have so many products containing so many different types of physical and chemical sunscreens with so many different types of bases - anhydrous, fancy moisturizers, basic lotions - that there is something you will be able to use. You will have to invest some time and money to find a product that your skin likes - I've been searching for years - but you will find something.
this recipe I made recently for my husband? I've used it for soothing various problems and I like it! I did tweak mine to include 10% aloe vera - good for post sun exposure - and added 2% hydrolyzed protein to the heated water phase and 2% panthenol to the cool down phase. Feel free to switch the stearic acid for cetyl alcohol for a slightly less thick but more glide-y product. And switch the oils if you wish!