Sunscreen and Skin Cancer – the Science
by The Environmental Working Group, Washington DC, USA
The first sunscreens were developed to prevent severe sunburn
for military personnel spending long hours under strong and
direct sunlight (Maceachern 1964). Today, they are associated
with a wide range of purported purposes, from reducing skin
aging and direct sun damage to decreasing the risk of skin
cancer. Yet expert opinions differ widely on the strength and
reliability of scientific evidence that supports these claims (Autier
2009; Draelos 2010).
The power of sunscreen to protect against sunburn is well known;
this is the feature of sunscreens identified as the Sun
Protection Factor or SPF. Yet, the wide availability of
sunscreens has allowed people with light-color skin to stay
outdoors longer, often aiming to get a tan or to maximize
burn-free time in the sun (Autier 2009; Lautenschlager 2007.
Expert’s recommendations to wear sunscreen are tempered. Skin
cancer rates continue to increase in the U.S. and other
countries. Studies do not provide evidence that sunscreen
protects against the deadliest form of skin cancer, and
scientists are not certain about which type of UV radiation, UVA
or UVB, is most dangerous and therefore most important for
sunscreen to block or absorb. Sobering statistics on skin cancer
raise basic questions about sunscreen efficacy:
Even though more people use sunscreen than ever before, the
incidence of skin cancer in the United States and other
countries continues to rise (Aceituno-Madera 2010; Jemal
2008; Osterlind 1992).
A number of studies conducted in the 1990s report higher,
not lower, incidence of the deadliest form of skin cancer,
malignant melanoma, among frequent sunscreen users (Autier
1995; Westerdahl 2000; Wolf 1994).
According to the American Cancer Society, malignant melanoma
accounts for only 3-4% of all skin cancer cases, but is
responsible for 75% of all deaths attributed to the disease
each year (ACS 2010) (See side-bar: “The 3 types of skin
To date, studies show that regular sunscreen use reduces
risk for squamous-cell carcinoma (SCC) but not other types
of skin cancer. SCC, a slow-growing, treatable cancer, is
estimated to account for just 16% of all skin cancers
The 3 Types of Skin Cancer
Skin cancer is the most common cancer in the United States,
accounting for nearly half of all cancer cases. One to 2 million
people develop skin cancer each year (Bikle 2008; Rogers 2010,
ACS 2010). A recent study estimated that the disease is five
times more prevalent in the U.S. population than breast or
prostate cancers (Stern 2010).
Precise numbers for skin cancer incidence in the U.S. are not
known, since non-melanoma skin cancer is usually excluded from
cancer registry statistics and, additionally, their incidence
varies by the geographical region (Rubin 2005). However,
according to a review published by the American Cancer Society,
among all the skin cancers 80% are basal-cell carcinoma (BCC),
16% are squamous-cell carcinoma (SCC), and 4% are malignant
melanomas, the deadliest form of skin cancer (Greenlee 2001).
Melanoma and Sunscreen: UVA, UVB or
For decades, sunscreens available on the market primarily
blocked UVB, the wavelength of ultraviolet radiation that causes
sunburns (Draelos 2010). Sunscreen manufacturers and sunscreen
users assumed that preventing or delaying sunburn would also
protect from other dangerous effects of the sun such as skin
Today, many experts believe that both UVA and UVB exposure may
contribute to melanoma risk (Garland 2003; Godar 2009).
Sunscreens produced over the past three decades that blocked UVB
but allowed higher UVA exposure may not have been able to
provide the necessary cancer protection (Draelos 2010) and may
have contributed to risk of melanoma in some populations (Gorham
Sunlight that reaches the surface of the Earth consists of
longer-wavelength UVA (315–400 nm), shorter wavelength UVB
(280–315 nm), visible light, and infrared light. UVB constitutes
3-5% of the total UV radiation that gets through the atmosphere,
while UVA constitutes 95-97%. UVB, which only penetrates the
outer skin layer, is the primary cause of sunburn (erythema or
redness) and non-melanoma skin cancer such as squamous cell
carcinoma (von Thaler 2010). In contrast, UVA can penetrate
deeper into the skin where it causes a different type of DNA
damage than does UVB (Cadet 2009).
Even though many sunscreens now include UVA filters, a large
number of products available in 2010 still fail to adequately
protect sunscreen users from UVA radiation.
A growing body of data points to UVA exposure as a significant
factor in melanoma development. But scientists still do not know
the relative importance of UVA and UVB in melanoma development (Donawho
1996; Setlow 1993), a knowledge gap that raises the importance
of broad-spectrum protection in sunscreens, with filters that
absorb both UVA and UVB radiation:
“Results from animal models, epidemiological studies, and
clinical observations suggest that UVA might play an
important role in the pathogenesis of malignant melanoma.”
Rünger 1999, Photodermatology, photoimmunology &
“Collectively, [current] data suggest a potential role for
UVA in the pathogenesis of melanoma.” Wang et al 2001,
Journal of the American Academy of Dermatology.
“The issue of [melanoma] action spectrum has been a subject
of debate, with some groups suggesting that the effect of
UVA is predominant in human melanoma with earlier groups
having suggested that UVB is the predominant cause of skin
cancer in general, although not necessarily melanoma in
particular.” Garland et al. 2003, Annals of Epidemiology.
“Although sunlight is known to cause melanoma, there has
been considerable controversy as to the importance of short
(UVB) and long (UVA) ultraviolet (UV) wavelengths in causing
melanoma, leading to uncertainty in how best to prevent this
cancer. This uncertainty has been compounded by the
difficulties in assaying the UVA protection abilities of
sunscreens, as compared to widely accepted measures of UVB
screening by the sun protection factor (SPF).” Lund &
Timmins 2007, Pharmacology and therapeutics.
“The [sunscreen’s] ability to prevent sunburns (as measured
by SPF) probably does not imply the ability to prevent
melanoma or basal cell carcinoma.” Autier 2009, British
Journal of Dermatology.
“The specific contribution of UVB and UVA radiation exposure
towards the risk of melanoma is controversial.” von Thaler
et al. 2010, Experimental Dermatology.
“There is also sufficient evidence of an increased risk of
ocular melanoma associated with the use of tanning devices.”
International Agency for Research on Cancer (IARC) 2009.
“Indoor tanning facilities in general deliver higher
relative intensities and higher proportions of UVA compared
with solar UV radiation.” IARC 2006.
Why Don’t Scientists Know More About
Sunscreen and Skin Cancer?
Three factors preclude drawing definitive conclusions about the
effects of sunscreens on skin cancer risk: 1) in parallel with
protection from sunburns, application of sunscreens has been
also associated with increased sun exposure, including usually
unexposed sites such as the trunk (Autier 2000; Dupuy 2005;
Stanton 2004); 2) early-generation sunscreens did not provide
significant or adequate UVA protection or possibly even
sufficient UVB protection (Diffey 2009; Lautenschlager 2007;
Osterwalder 2009); 3) sunscreen use in the populations studied
may not have been consistent or sufficient to provide the
protection from melanoma (Bech-Thomsen 1992; Thieden 2005).
Published studies have examined the correlation between
sunscreen use and the development of the three most common forms
of skin cancer: basal cell carcinoma, squamous cell carcinoma,
and malignant melanoma. In 2000, International Agency for
Research on Cancer (IARC) reviewed available data and concluded
Sunscreen use may decrease the occurrence of squamous cell
Sunscreen use has no demonstrated influence on basal cell
In intentional sun exposure situations, sunscreen use may
increase the risk of melanoma (IARC 2001a; reviewed in
Studies conducted over the past decade have confirmed that
regular sunscreen use lowers the risk of squamous cell carcinoma
(Gordon 2009; van der Pols 2006), similar to studies completed
in the 1990s (Green 1999). Regular sunscreen application also
diminishes the incidence of solar keratosis (also known as
actinic keratosis), a type of sun-induced skin changes that may
become precursors to squamous cell carcinoma (Naylor 1995;
For basal cell carcinoma, follow up studies reported a slight
and not-statistically significant decrease in risk associated
with sunscreen use (Pandeya 2005; van der Pols 2006). Thus, for
this cancer type, data on sunscreen benefits remain negative or
equivocal (Hunter 1990; Rosenstein 1999; Rubin 2005).
However, from the public health perspective, physicians are most
concerned about malignant melanoma, the deadliest type of skin
cancer (Lund 2007; World Health Organization 2006). Sunburns are
an important risk factor for melanoma (Leiter 2008).
Intermittent, severe sunburns in childhood have been considered
to pose the greatest risk, although sunburn during all life
periods likely contributes to melanoma development (Autier 1998;
State of the evidence: human epidemiology studies of melanoma
risk in sunscreen users
Individual studies provide conflicting evidence on the role of
sunscreen in melanoma risk. Studies in Sweden, Belgium, France,
Germany, Austria, and New York state report an elevated risk of
melanoma in sunscreen users (Autier 1998; Beitner 1990; Graham
1985; Westerdahl 2000; Wolf 1998). In contrast, studies in
Spain, Brazil and San Francisco, California report decreased
risk of melanoma in sunscreen users (Bakos 2002; Espinosa Arranz
1999; Holly 1995; Rodenas 1996).
A 2000 IARC assessment of 15 studies on sunscreen and melanoma
revealed conflicting evidence regarding associations between
sunscreen and melanoma, with 3 studies showing significantly
lower risks on melanoma associated with sunscreen use, 8 studies
finding significantly higher risks associated with sunscreen
use, and 4 studies reporting no effect (IARC 2001, reviewed in
Dennis 2003; Diffey 2009; Gorham 2007; Huncharek 2002).
Some scientists have combined the data from multiple sunscreen
studies in what are called “meta-analyses,” which allows them to
assess larger or specialized groups of sunscreen users. A
meta-analysis of melanoma studies conducted by University of
Iowa scientists in 2003, reported a lack of overall association
between melanoma risk and sunscreen use (Dennis 2003).
The Iowa researchers suggested that findings of elevated risk in
a large group of studies conducted in Europe and U.S. may have
been due to confounding effects, such as differences in skin
sensitivity to sunlight among people with lighter or darker
skin. Sunscreens are more likely to be used by people most at
risk of quick sunburn (Diffey 2009; Geller 2002, a group at
higher risk for melanoma (Dubin 1986).
In contrast to the conclusion from the Iowa group, a
meta-analysis conducted by University of California San Diego
scientists in 2007 found a link between the location of the
study (high or low latitude from the equator) and the risk of
melanoma in relationship to sunscreen use. According to this
analysis, in populations living at latitudes below 40o from the
equator, the use of sunscreens was associated with a
non-significant decreased risk of melanoma, while populations in
higher latitudes faced a statistically significant increase in
melanoma risk linked with sunscreen use (Gorham 2007).
Skin pigmentation may have been the reason for these latitude
effects (Gorham 2007). Studies finding protective effects of
sunscreens generally included Mediterranean populations or
populations with prevalent Mediterranean ancestry, which have
higher degree of constitutive pigmentation. On the other hand,
studies conducted in light-skinned populations residing far from
the equator (above 40o latitude) generally found a statistically
significant 60 percent increase in melanoma risk (Espinosa
Arranz 1999; Rodenas 1996).
Experts generally agree that the tendency of sunscreen users to
spend more recreational time in direct sunlight and to wear less
protective clothing may increase the amount of sun damage that
leads to melanoma (Autier 2009; Draelos 2010; Gorham 2007).
Additionally, scientists still do not know which wavelengths of
sunlight drive melanoma development (Donawho 1996). Thus,
historical absence of broad-spectrum UV protection in sunscreen,
especially UVA protection, may have contributed to melanoma
development or at least to the lack of evidence for a decrease
in melanoma risk (Garland 2003; Godar 2009).
With so little known with confidence about sunscreen and skin
cancer, it is no wonder that many experts are now recommending
clothing and shade, not sunscreen, as primary barriers from sun
exposure. For full details on the report, please click
The above information should not be treated as a substitute for the
medical advice of your own doctor or any other health care