SPF of white cotton t-shirts

[Tim McNamara]

I dunno, I have been out in the sun in a white cotton T-shirt for 10
hours or more in midsummer, and never got sunburned under it. I'd say
that's an SPF above 60, at least. In fact, I've never gotten
sunburned through clothing in the past 45 years. I suppose one could
wear something flimsy enough and get sunburned.

 

[Peter]

Tim McNamara wrote:
> I dunno, I have been out in the sun in a white cotton T-shirt for 10
> hours or more in midsummer, and never got sunburned under it. I'd say
> that's an SPF above 60, at least.

10 hours protected by an SPF of 60 would be equivalent to only 10
minutes while unprotected. Are you so sensitive to sunlight that
walking outside for 10 minutes gives you a sunburn on uncovered
parts of your arms and legs?

I agree that my experience has been that T-shirts generally
protect much better than the SPF of 5 that's been mentioned
in some posts and articles, but I have gotten slightly
tanned through light-colored clothing and would guess the
effective SPF is more in the 10 - 20 range depending on the
type of fabric.

The measurements that came out with the SPF 5 figure must
have been done on some very thin material.

 

[David Damerell]

Patrick Lamb <[email protected]> wrote:
>My wife makes fun of my "farmer's tan." Parts of my body regularly
>covered by clothes, like a t-shirt, are pale, while uncovered parts of
>my body are tan (or red, depending on the week). Why do you think I'm
>pale? I think it's because a shirt of any type blocks the sun.

I think everyone knows this. The question is, _why_ does this happen,
given that measurements suggest the results would be otherwise?
--
David Damerell <[email protected]> Kill the tomato!

 

[Trevor Jeffrey]

OliverS wrote in message ...
>
>I recall reading a news article a while ago about a dermatologist who
>was puzzled by his daughter's striped sunburn. It seems she was wearing
>a black and white striped bathing suit, and the white stripes were
>passing more rays than the black stripes which were absorbing them. In
>other words, although white reflects, it also transmits.

It has to be remembered that those who live in N.African deserts generally
tend to wear two layers of dark clothing. The dark clothing re-radiates the
heat from the body. I notice this is a burn and not a tan.

Trevor

 

[Pat Lamb]

David Damerell wrote:
> Patrick Lamb <[email protected]> wrote:
>
>>My wife makes fun of my "farmer's tan." Parts of my body regularly
>>covered by clothes, like a t-shirt, are pale, while uncovered parts of
>>my body are tan (or red, depending on the week). Why do you think I'm
>>pale? I think it's because a shirt of any type blocks the sun.
>
>
> I think everyone knows this. The question is, _why_ does this happen,
> given that measurements suggest the results would be otherwise?

Faulty measurement equipment? Faulty measurement technique?

I don't really know, don't really care. It's the business of the people
making these claims to explain why their results don't match reality.

Pat

 

[David Damerell]

Pat Lamb <[email protected]> wrote:
>David Damerell wrote:
>>Patrick Lamb <[email protected]> wrote:
>>>My wife makes fun of my "farmer's tan." Parts of my body regularly
>>>covered by clothes, like a t-shirt, are pale, while uncovered parts of
>>>my body are tan (or red, depending on the week). Why do you think I'm
>>>pale? I think it's because a shirt of any type blocks the sun.
>>I think everyone knows this. The question is, _why_ does this happen,
>>given that measurements suggest the results would be otherwise?
>Faulty measurement equipment? Faulty measurement technique?
>I don't really know, don't really care.

Perhaps then you should shut up, and let the people who _are_ interested
discuss it without pointless interruptions.
--
David Damerell <[email protected]> Kill the tomato!

 

[Benjamin Weiner]

Terry Morse <[email protected]> wrote:
> Fx199 wrote:

> > >http://www.cottoninc.com/textilechemistry/homepage.cfm?page=616
> > >Summary:
> > >undyed white cotton = little or no protection

> > oh come one now...take two bald guys...put em out in the sun, wrap one's head
> > up in the "undyed cotton", lotion on the other guy ...who's gonna get burnt?

> If the t-shirt is one layer thick, the guy with the t-shirt on his
> head will get burnt. UV meters don't lie.

But extrapolating the results of an experiment beyond experience does
mislead. Experience indicates that white T-shirts are effective at
preventing sunburn. I don't know how many hours it takes to get burnt
through a white shirt, since it's never happened to me, but it's
significantly better than no protection. (Somebody else posted a
story about a kid getting burnt through a white swimsuit. I'm sure that
can happen but swimsuits are thinner than T-shirts and it was likely a
long exposure.) We don't need more hypotheticalfears to worry about -
although if the ozone layer keeps going away, switching to darker
T-shirts may be in order in the future.

Why do white T-shirts appear to be as effective as SPF-rated sunscreen
in practical use? Probably because T-shirts don't sweat, wash, or
wipe off, and because people don't slather sunscreen on as thickly as
SPF testers do. This is the part of the experiment that a UV meter
can't check. IMO, the practical matter is that the OP doesn't need to
worry.

 

[Terry Morse]

Benjamin Weiner wrote:

> But extrapolating the results of an experiment beyond experience does
> mislead. Experience indicates that white T-shirts are effective at
> preventing sunburn. I don't know how many hours it takes to get burnt
> through a white shirt, since it's never happened to me, but it's
> significantly better than no protection.

Note the pubmed article I referenced which stated that a washed and
shrunk cotton shirt has 51% higher UPF than a new shirt:

http://tinyurl.com/42owq

Summary of UPF:

white untreated cottton: 4.94
laundered 5 times: 7.46
UV treated: 25
dyed blue: 32

Just to add another anecdote, I've been burned through a laundered
white t-shirt while snorkeling in the Carribean. That took about 1.5
hours.
--
terry morse Palo Alto, CA http://bike.terrymorse.com/

 

[Fx199]

>Just to add another anecdote, I've been burned through a laundered
>white t-shirt while snorkeling in the Carribean. That took about 1.5
>hours.
>--
>terry morse Palo Alto, CA http://bike.terrymorse.com/

Next time I'm cycling underwater I'll think about that

 

[Ray Heindl]

Tim McNamara <[email protected]> wrote:

> I dunno, I have been out in the sun in a white cotton T-shirt for
> 10 hours or more in midsummer, and never got sunburned under it.
> I'd say that's an SPF above 60, at least. In fact, I've never
> gotten sunburned through clothing in the past 45 years. I suppose
> one could wear something flimsy enough and get sunburned.

In an article about sunscreens a while back, Consumer Reports claimed
that a Hanes Beefy-T has an SPF of about 30, if memory serves.
Unfortunately I don't remember what color they tested.

--
Ray Heindl
(remove the Xs to reply to: [email protected])

 

[Terry Morse]

Fx199 wrote:

> >Just to add another anecdote, I've been burned through a laundered
> >white t-shirt while snorkeling in the Carribean. That took about 1.5
> >hours.
>
> Next time I'm cycling underwater I'll think about that

Just goes to show you how dubious anecdotes can be. Although I
wasn't underwater the whole time.
--
terry morse Palo Alto, CA http://bike.terrymorse.com/

 

[Fritz M]

[email protected] (Fx199) wrote:

> that's not the kind of material we deal with in every day life, or redheads
> wouldn't be able to wear white T-shirts.

My wife, a redhead, has been severely burned through white cotton Ts.

That said, they do seem to provide more protection than the SPF 5-9
that's cited. I spend a couple of hours a day in the sun and my
covered parts are significantly paler than my uncovered parts.

RFM

 

[Fritz M]

[email protected] (Fx199) wrote:

> that's not the kind of material we deal with in every day life, or redheads
> wouldn't be able to wear white T-shirts.

My wife, a redhead, has been severely burned through white cotton Ts.

That said, they do seem to provide more protection than the SPF 5-9
that's cited. I spend a couple of hours a day in the sun and my
covered parts are significantly paler than my uncovered parts.

RFM

 

[Fx199]

>Subject: Re: SPF of white cotton t-shirts
>From: Terry Morse [email protected]
>Date: 8/18/2004 5:40 PM US Eastern Standard Time
>Message-id: <[email protected]>
>
>Fx199 wrote:
>
>> >Just to add another anecdote, I've been burned through a laundered
>> >white t-shirt while snorkeling in the Carribean. That took about 1.5
>> >hours.
>>
>> Next time I'm cycling underwater I'll think about that
>
>Just goes to show you how dubious anecdotes can be. Although I
>wasn't underwater the whole time.



We also get intermittent shade while cycling unlike the ocean, and your shirt
was obviously soaking wet.
You're supposed to wear a diveskin..a lycra shirt and tights, or suit.

 

[Fritz M]

[email protected] (Fx199) wrote:

> that's not the kind of material we deal with in every day life, or redheads
> wouldn't be able to wear white T-shirts.

My wife, a redhead, has been severely burned through white cotton Ts.

That said, they do seem to provide more protection than the SPF 5-9
that's cited. I spend a couple of hours a day in the sun and my
covered parts are significantly paler than my uncovered parts.

RFM

 

[Terry Morse]

Fx199 wrote:

> We also get intermittent shade while cycling unlike the ocean, and your shirt
> was obviously soaking wet.

Shade? I sure could have used some of that last weekend in the
Eastern Sierra. The road from Big Pine to Schulman Grove was a solar
oven. I didn't know I could sweat that much. Three bottles were not
enough for a 2.5-hour climb:

http://bike.terrymorse.com/esierra0408/pages/IMG_0597.html

> You're supposed to wear a diveskin.

I was younger then and less informed about the sun.
--
terry morse Palo Alto, CA http://bike.terrymorse.com/

 

[Fx199]

>> You're supposed to wear a diveskin.
>
>I was younger then and less informed about the sun.

Sounds like you're still *****in, and maybe even still frying

;-D

 

[jbuch]

You can only see visible light. You can't see infared... long wavelength
light - "heat".

You can't see Ultraviolet either.

It is the ultraviolet rays with wavelengths shorter than 0.4 microns
that cause tanning and other skin degradation.

Your camera light meter probably can't see this wavelength either... or
if it can, it is so flooded by the much more abundant visible light that
it doesn't accurately record the UV that causes skin damage.

You can't see the sunlight that causes skin cancer or tanning.

There is probably not much difference in SPF of a green Tshirt and a
white one.

Jim

wle wrote:
> recently, i read that white cotton t shirts have an SPF of about 5.
>
> since i ride about 2 hours a day, all year, that;s all i wear in the summer.
> [don;t want to have 7-10 bike jerseys at $xx a pop.]
>
> i tried to measure the SPF with my camera.
> i discovered they cut the [visible] light by
> about 1 f stop, which as i understand SPF would be about SPF 1.
>
> [the published data allegedly refers to UV light.]
>
> so then i started thinking about my arms.
> they are tan below the t shirt line, much whiter above.
> yet i wear sun screen every day, SPF 30+.
>
> yet - here is the question -
> if the t shirt really has such a low SPF, why does it appear to do much
> more screening than the sun screen?
>
> the t shirts are clearly screening more than the sunscreen.
> but how?
>
> wle.


--
................................


Keepsake gift for young girls.
Unique and personal one-of-a-kind.
Builds strong minds 12 ways.
Guaranteed satisfaction
- courteous money back
- keep bonus gifts

http://www.alicebook.com

 

[Patrick Lamb]

On 18 Aug 2004 19:19:13 +0100 (BST), David Damerell
<[email protected]> wrote:

>Pat Lamb <[email protected]> wrote:
>>David Damerell wrote:
>>>Patrick Lamb <[email protected]> wrote:
>>>>My wife makes fun of my "farmer's tan." Parts of my body regularly
>>>>covered by clothes, like a t-shirt, are pale, while uncovered parts of
>>>>my body are tan (or red, depending on the week). Why do you think I'm
>>>>pale? I think it's because a shirt of any type blocks the sun.
>>>I think everyone knows this. The question is, _why_ does this happen,
>>>given that measurements suggest the results would be otherwise?
>>Faulty measurement equipment? Faulty measurement technique?
>>I don't really know, don't really care.
>
>Perhaps then you should shut up, and let the people who _are_ interested
>discuss it without pointless interruptions.

I do hope this wasn't supposed to be a snappy comeback. Rather than
displaying your intellect, it displayed your density. Mine was a
pointed comment in a pointless discussion.

The starting point of this thread was an allegation that white cotton
t-shirts have a rather low SPF equivalent. Two posters, further down
the thread, report single instances of sunburn through such a t-shirt.
The overwhelming majority of people wearing t-shirts don't get burned.
Therefore, the alleged low SPF is cast into doubt.

I could offer speculation, and perhaps more intelligent speculation
than most, about why the observed protection of t-shirts exceeds the
reported low value. However, that would be strictly speculation.
Nobody's come forth with enough information to make this an
intelligent discussion yet.

If you want to flap your gums (or fingers), continue as you were. If
you'd prefer to have a discussion which might result in something
useful, start asking or answering some good questions, such as:

(1) What kind of t-shirt are we talking about? Brand? Areal
density, before and after washing?

(2) Was a calibrated UV meter being used to test the absorbance?

(3) What waveband was tested?

(4) Did the experimental setup account for backscatter?

(5) If we're going to talk about the two anecdotal instances where
sunburn occurred through the t-shirt, we need information about the
t-shirt in question (was it a beefy Hanes t or a thin, cheap shirt?)
and information from which we can deduce likely UV radiation levels,
including time of year, time of day, latitude, and relative humidity
levels. Similar information would be useful for all negative reports.

So decide. Either inject some level of rigor or admit we're all idly
chatting.

BTW, either way, I think it's reasonable to ask for more details about
where the data came from. If the discussion is just over, "Will I get
sunburn wearing a white t-shirt?" it can't be answered just from
experiential data and some magazine's counterclaim. That question
can't be answered without the answer to my question (1), above. If
you want to get down to details and learn some facts, you'd still need
the same information.

Pat

Email address works as is.