When to use sunscreen

[Zelenius]

I'm an outdoorsy type of person and I have very fair skin. It burns easily, so I usually apply a lot of sunscreen when I go outside in the middle of the day during the summer months(I'm in the north-east U.S).

That said, I have some questions about when to use sunscreen:

1) Do I have to use it before 10 AM or after 4 PM? Does sunlight still cause damage after 4 PM even if it doesn't burn the skin?

2) Do I have to wear sunscreen on cloudy days?

3) Do I have to wear sunscreen on my face in the middle of the day during the winter if my face is going to be exposed?

 

[rjh01]

4) How much does sunscreen slow down Vitamin D production? I am deficient in Vitamin D.

 

[Dr. Keith]

Here is a pretty good source of info.

I'm an outdoorsy type of person and I have very fair skin. It burns easily, so I usually apply a lot of sunscreen when I go outside in the middle of the day during the summer months(I'm in the north-east U.S).

That said, I have some questions about when to use sunscreen:

1) Do I have to use it before 10 AM or after 4 PM? Does sunlight still cause damage after 4 PM even if it doesn't burn the skin?

They don't address that in the link above, but I would think that if it isn't enough to burn you are probably OK. I've gotten a burn on a clear morning before, but it did take a bit longer.

2) Do I have to wear sunscreen on cloudy days?

According to the link above you can still get 80% of the UV on a cloudy day. I believe that as I have gotten nasty burns on cloudy days in the past.

3) Do I have to wear sunscreen on my face in the middle of the day during the winter if my face is going to be exposed?

I think that is similar to the dawn and dusk question, the angle of the sun will certainly impact your exposure, but I don't know how much.

4) How much does sunscreen slow down Vitamin D production? I am deficient in Vitamin D.

According to the link above it will. Skin cancer risk v. Vitamin D deficiency. I guess that will depend on how well you can impact your Vit D deficiency with diet and supplements.

ETA: Here is another good source of info. If you search around on your own I would take anything from the EWG (Environmental Working Group) with a grain of salt. When I was paid to pay attention to what they were saying I often found their information misleading. But it would sometimes require a lot of discussions with scientists in the field to pick apart how they were misleading. They were carefully misleading, I guess you could say. At least, that was my experience when I was paid to care about such things.

 

[BowlOfRed]

1) Do I have to use it before 10 AM or after 4 PM? Does sunlight still cause damage after 4 PM even if it doesn't burn the skin?

The time of the day isn't as specifically relevant as the angle of the sun and the opacity of the sky. 4PM in winter is significantly different than 4PM in summer.

It's not that you can't get burn/damage, just that the time to do so has increased significantly due to attenuation.

There's a chart of UV irradiance vs time of day at the bottom of this page:
http://uvb.nrel.colostate.edu/UVB/publications/uvb_primer.pdf

2) Do I have to wear sunscreen on cloudy days?

Depends on the clouds. See:
http://www.epa.gov/sunwise/uvicalc.html
but also:
http://www.americanscientist.org/issues/pub/sunshine-on-a-cloudy-day

3) Do I have to wear sunscreen on my face in the middle of the day during the winter if my face is going to be exposed?

It's unlikely the sun is going to be at a high angle during the winter. That's going to increase UV attenuation. But some will be present. You're not silly for wearing it.

 

[s4zando]

Wrt #4, I remember a radio program which suggested putting sunscreen on after 15 minutes of regular exposure, simply to ensure adequate vitamin d absorption. Sorry, no links.

 

[Dr. Keith]

The time of the day isn't as specifically relevant as the angle of the sun and the opacity of the sky. 4PM in winter is significantly different than 4PM in summer.

It's not that you can't get burn/damage, just that the time to do so has increased significantly due to attenuation.

There's a chart of UV irradiance vs time of day at the bottom of this page:
http://uvb.nrel.colostate.edu/UVB/publications/uvb_primer.pdf



Depends on the clouds. See:
http://www.epa.gov/sunwise/uvicalc.html
but also:
http://www.americanscientist.org/issues/pub/sunshine-on-a-cloudy-day




It's unlikely the sun is going to be at a high angle during the winter. That's going to increase UV attenuation. But some will be present. You're not silly for wearing it.

Very cool links! Thanks for adding something useful over top of my hand-wavey BS above.

 

[Dr. Keith]

Wrt #4, I remember a radio program which suggested putting sunscreen on after 15 minutes of regular exposure, simply to ensure adequate vitamin d absorption. Sorry, no links.

Yeah, that's a tough balance. The sunscreen folks say to add 30 minutes before exposure if exposure will be more than 20 minutes. I think the best solution is to have a short commute, bald head and a convertible. Throw in a quick lunch outing if levels dip.

 

[Zelenius]

Here is a pretty good source of info.

The time of the day isn't as specifically relevant as the angle of the sun and the opacity of the sky. 4PM in winter is significantly different than 4PM in summer.

It's not that you can't get burn/damage, just that the time to do so has increased significantly due to attenuation.

There's a chart of UV irradiance vs time of day at the bottom of this page:
http://uvb.nrel.colostate.edu/UVB/pu...uvb_primer.pdf

Very useful info, thanks! I'm determined to never get another sunburn, even with all the distance running I do.

 

[joller]

THis is the website I check daily (well, outside of winter, which is right now):
http://www.arpansa.gov.au/uvindex/realtime/can_rt.htm
The main website and sites it links to have a lot of explanation about the specifics of when it is safe, how to pretect yourself, and vitamin-d deficiency:
http://www.actcancer.org/sun-smart/vitamin-d.aspx
In general, in Australia, ' a few minutes' per day in the sun is enough to avoid vitamin d problems.

http://www.cancer.org.au/preventing-cancer/sun-protection/vitamin-d/

I take my kids for around 60 minutes walk every day, I always wait until the UV index drops below 5 before we go, which in the summer months is usually around 5pm where I live (max daily UV of 12 or 13 is normal in Australia during summer months). UV 5 isn't necessarilly safe enough to not wear sunscreen, but at that stage of the day the UV drops off fairly sharply, so the total exposure I get for the whole walk is quite managable, and we don't get burnt. I usually wear a hat just in case.

 

[Alareth]

What?

No one has posted this?



I'm disappointed in all of you.

 

[Jrrarglblarg]

I live at 5000+ feet, so I put on SPF 30 (or higher) sunscreen about a half hour before dawn on National Guard weekends where I will be outdoors, and reapply about every hour or so. This means I might only get a little bit burned.

A few years ago I was in South Carolina at about 324' above sea level. I went out to the field for a 3-day FTX and forgot sunscreen. I suffered more from using a cheap battery powered electric razor than I did from solar exposure.

 

[rjh01]

Thanks to those that replied to my question. I will have a look at the links.

 

[Skeptic Ginger]

...I think the best solution is to have a short commute, bald head and a convertible. Throw in a quick lunch outing if levels dip.

I little self reflection there?

 

[Skeptic Ginger]

I'd rather take a vitamin D supplement and block more skin-aging sun, but it gets tiring putting the sunscreen sometimes. So in a hurry, I grab the sunhat and I have a long sleeved very light weight shirt that I use to cover my arms if it isn't too hot. I don't button it up.

 

[Zelenius]

4) How much does sunscreen slow down Vitamin D production? I am deficient in Vitamin D.

Thanks for asking this. I was going to ask something about vitamin D too, but didn't want to ask too many questions. Right now I am back to taking vitamin D pills, but only once or twice a week because of how much sunblock I use(even a few minutes of sunlight in the middle of the day during the summer can cause damage). I usually only take vitamin D pills during the winter because of how far north I am. It's probably the only supplement worth taking, since I can't even achieve the RDA through food alone.

Actually it is possible to get a lot of vitamin D through food if you eat liver on a regular basis or if you leave mushrooms in sunlight for a few hours.

So if you hate taking pills, try the mushroom trick, as I call it.

Many people living in the northern hemisphere, however, suffer from lower levels of vitamin D during the fall, winter and spring. Fortunately, you can make your own supply of vitamin D-enriched mushrooms by simply exposing them to sunlight. You can sun dry or UV-zap store-bought or homegrown shiitake, maitake, button, and many other mushroom species. My personal preference is home grown organic shiitake. The high vitamin D levels generated will last for more than a year. Surprisingly, even sliced and dried mushrooms—including wild ones picked the year before—will soar in vitamin D when placed outdoors under the sun. Now, the summer time, from June until September, is the best seasonal window for people in northern latitudes to make vitamin D enriched mushrooms!

 

[Fishstick]

So if you hate taking pills, try the mushroom trick, as I call it.

You can VitD in droplet or ampule form. 5 - 10 drops a day will more than satisfy your need - I had a pretty major deficiency as well, but now I start my day off with a glass of milk with 5 drops of VitD in it.

It's also pretty cheap, a month's worth of daily droplets is 3 euro.

 

[Steve001]

I'm an outdoorsy type of person and I have very fair skin. It burns easily, so I usually apply a lot of sunscreen when I go outside in the middle of the day during the summer months(I'm in the north-east U.S).

That said, I have some questions about when to use sunscreen:

1) Do I have to use it before 10 AM or after 4 PM? Does sunlight still cause damage after 4 PM even if it doesn't burn the skin?

No [visible] sunlight does not hurt your skin, but UV does, so yes.

2) Do I have to wear sunscreen on cloudy days?

Generally yes. Clouds don't block UV light well.

3) Do I have to wear sunscreen on my face in the middle of the day during the winter if my face is going to be exposed?

Generally yes.

 

[phunk]

3) Do I have to wear sunscreen on my face in the middle of the day during the winter if my face is going to be exposed?

If you're out in the open and there's snow on the ground, definitely. The worst sunburn I've ever had on my face was in the middle of February while snowboarding. While the low sun angle may reduce it, the reflected UV off snow will increase it significanlty.

 

[Fishstick]

If you're out in the open and there's snow on the ground, definitely. The worst sunburn I've ever had on my face was in the middle of February while snowboarding. While the low sun angle may reduce it, the reflected UV off snow will increase it significanlty.

I can add to this. I'm probably one of the last guys who has regular glasses with uv-reactive particles - my glasses go darker depending on the amount of UV.
Bright, cloudy days are the most useful times where they go dark, especially during winter where snow would otherwise blind me even though there's no direct sun'light'. Even if you don't have actual bright skies and sun, there's still a ton of UV that makes it to earth.

There's a reason skiiers wear goggles and apply sunscreen and still get tans - cloudy skies and a snowy environment still reflect a lot of UV, enough to cause sunburn.

 

[Mark6]

Also on a boat. UV reflects off sea surface quite well, and a cool cloudy day can deceive you into thinking sunscreen is not necessary. On a boat during day - yes it is necessary!