Sunscreens With Iron Oxide - Importance & Benefits

What Are The Benefits Of Iron Oxides in Sunscreen?

Sunscreens help filter out ultraviolet (UV) light using two main types of ingredients. Organic sunscreens, also known as chemical sunscreens, work by absorbing UV light. Chemical sunscreens include ingredients such as oxybenzone, avobenzone, octisalate, octocrylene, homosalate, ecamsule, and octinoxate.

Inorganic, or physical sunscreens contain metal oxides such as zinc oxide and titanium dioxide that reflect and scatter UV light. Zinc oxide provides better UVA protection than titanium dioxide, including protection against UVA 1 (340-400 nm), but it is less efficient than titanium against UVB radiation.[1] Titanium dioxide protects against UVA 2 (320-340 nm) and UVB protection, but does not protect against UVA 1 radiation in the way zinc oxide does.[2]

Ultraviolet Radiation and Visible Light

There are many different types of rays in sunlight. Ultraviolet radiation is the most damaging to our skin and has wavelengths shorter than visible light, making it invisible to the naked eye. Within the UV spectrum, there are UVA, UVB, and UVC rays.

UVC rays (100-290 nm) are the shortest wavelength and are mostly absorbed in the ozone layer. Generally, they do not reach the earth’s surface and thus are not thought to be major contributors to skin damage by the sun.

UVB rays (290-320 nm) are shorter wavelengths that can penetrate the atmosphere. They cause damage to the superficial layers of the skin, resulting in reddening of the skin (sunburns), and DNA damage, which contributes to the development of skin cancers.[3] SPF ratings on sunscreens refer mostly to protection against UVB rays.

UVA rays (320-400 nm) are longer wavelengths that can penetrate the atmosphere and can be further broken up into UVA 1 (340-400 nm) and UVA 2 (320-340 nm) wavelengths. These rays penetrate deeper into the skin and can therefore damage collagen, resulting in premature aging and wrinkles. UVA rays can also damage DNA and thus play a role in the development of skin cancers.[3] Because the SPF value is based primarily on UVB rays, the “PA+” rating system was developed in Japan to represent how much UVA protection a product has. However, there are issues in how the value is achieved and applied, so regulatory agencies in Europe and the US use the term “broad-spectrum” to ensure a product has coverage against UVA and UVB wavelengths.

Visible light (400-700 nm) can penetrate much deeper into the skin than UVA or UVB rays. Though not traditionally thought of as damaging to the skin, visible light can exert negative effects through the production of reactive oxygen species, causing indirect DNA damage.[4] In people with darker skin, visible light can cause more potent and long-lasting pigmentation compared with UVA1 radiation.[5, 6] Most sunscreens do not protect against visible light. 

Shorter wavelengths of visible light (blue) closest to the UV range are more concerning than longer wavelengths (red) when it comes to sun damage, since they are more energetic. Wavelengths in the blue region (~415 nm) have been found more likely to induce hyperpigmentation compared to wavelengths in the red region (630 nm)[7] and contribute to relapse of pigmentary disorders such as melasma, especially in darker-skinned individuals.[8] 

What Does SPF Mean?

SPF (Sun Protective Factor) is a relative measure of how long a sunscreen will protect you from UVB. For example, if your skin normally burns after 10 minutes in the sun, using an SPF 15 sunscreen will theoretically allow you to stay in the sun for a factor of 15 times longer, or 150 minutes, without burning. However, this can be altered by how much sunscreen is applied, the length of time spent in the sun, time of day, weather conditions, activities, and geographic location.

What Are Micronized Sunscreens?

Due to their opaque nature that often leaves a “white cast” on skin that is undesirable to consumers, zinc oxide and titanium dioxide are now frequently broken down into smaller nanoparticles (10-200 nm) to minimize their white appearance, and this is termed “micronized.” However, due to their smaller particle size, protection is shifted towards shorter wavelengths and do not protect against visible or blue light.[9]

Because of the small particle size, there is potentially an increased risk of systemic absorption, leading to concerns about their safety. Though studies have demonstrated micronized zinc oxide and titanium dioxide do not penetrate into deeper layers of the skin,[10, 11] the risk of long-term exposure and absorption has yet to be established. Finally, micronized particles tend to clump together, leaving areas of sun-exposed skin if not properly applied. 

What is the Cosmetic Role of Iron Oxide?

Most physical sunscreens consist of zinc oxide and titanium dioxide that act as physical blockers of UV light and thus can leave a whitish residue on skin that is cosmetically unappealing. Titanium dioxide has a smaller particle size and a higher refractive index than zinc oxide, which causes it to appear whiter on the skin. Iron oxide has gained popularity as an addition to physical sunscreens for its natural reddish hue, which serves a cosmetic role in improving the “white cast” of zinc and titanium dioxide and easily blends in with skin tones.

How do Iron Oxides Protect Us from the Sun?

Iron oxide can be added to physical sunscreens to increase the absorption and protection against visible light and UVA radiation. While titanium dioxide and zinc oxide have good absorption in the UV range, they do not confer protection in the visible light range if they are micronized.

Iron oxide is effective at absorbing visible light. One study by Kaye et. al showed that the addition of iron oxide to physical sunscreens such as zinc oxide or titanium dioxide transmits less light and thus provides greater photoprotection than either zinc oxide or titanium dioxide alone.[12]

Iron oxide is effective at protecting against UVA light.[13, 14] When combined with zinc oxide, iron oxide works synergistically to reduce the amount of UVA radiation transmitted to the skin to as little as 1.5%.[2]

Table 1. UV and Visible Light Protection by Zinc Oxide, Titanium Dioxide, and Iron Oxide

 

UVB (290-320 nm) protection

UVA 2 (320-340 nm) protection

UVA 1 (340-400 nm) protection

Visible Light (400-780 nm) protection

Non-micronized Zinc Oxide

Yes

Yes

Yes

Yes

Micronized Zinc Oxide

Yes

Yes

Yes

No

Non-micronized Titanium Dioxide

Yes

Yes

No

Yes

Micronized Titanium Dioxide

Yes

Yes

No

No

Iron Oxide

No

Yes

Yes

Yes

Iron Oxide’s Role in Hyperpigmentation Disorders

Hyperpigmentation disorders such as melasma and post-inflammatory hyperpigmentation affect millions of people worldwide. Common factors contributing to these disorders include genetic predisposition, female sex hormones, and exposure to UV light; however, it has also been found that visible light plays a role in the development of melasma.[15] Traditional chemical and physical sunscreens on the market provide defense against UV light, but do not normally protect against visible light, with the exception of non-micronized physical sunscreens. 

Iron oxides can be added to existing sunscreens to protect against hyperpigmentation caused by visible light.[15] Two randomized, double-blind controlled clinical trials to date have shown sunscreens with iron oxide to be significantly more efficient in treating and preventing melasma than classical UV sunscreens containing only titanium dioxide, zinc oxide, or other chemical filters that do not protect against visible light.[14, 16]

Where Can I find Sunscreens with Iron Oxide?

There are many brands for Mineral Sunscreens With Iron Oxide on the market that contain iron oxide, with fewer brands that contain both iron oxide and non-micronized zinc oxide or titanium dioxide (Table 2).

Table 2. Micronized and Non-micronized Sunscreens Containing Iron Oxide

Brand

% Titanium dioxide and Zinc oxide

Micronized or Non-micronized

Cotz Face Natural Skin Tone

Titanium dioxide 8%; Zinc Oxide 3.8%

Micronized

Tizo 3 Tinted Face Mineral Sunscreen

Titanium dioxide 8%; Zinc Oxide 3.8%

Micronized

Coola Mineral Face Matte Tint Moisturizer

Titanium dioxide 3.2%; Zinc Oxide 1.8%

Micronized

Skinceuticals Physical Fusion UV Defense

Titanium dioxide 6%; Zinc Oxide 5%

Micronized

Neostrata

Titanium dioxide 7%; Zinc Oxide 6%

Micronized

Exuviance Sheer Daily Protector

Titanium dioxide 7%; Zinc Oxide 6%

Micronized

Supergoop Smooth and Poreless 100% Mineral Matte Screen

Titanium dioxide 0.7%; Zinc Oxide 17%

Micronized

SkinMedica Essential Defense Mineral Shield

Titanium dioxide 5%; Zinc Oxide 6%

Micronized

MDSolarSciences Mineral Crème

Titanium dioxide 2%; Zinc Oxide 17%

Micronized

EltaMD UV Physical Tinted Facial Suncreen

Titanium dioxide 7%; Zinc Oxide 9%

Micronized zinc

Australian Gold Botanical Sunscreen Tinted Face Mineral Lotion

Titanium dioxide 4%; Zinc Oxide 4%

Micronized

Clinique Pep-Start Daily UV Protector

Titanium dioxide 6.3%; Zinc Oxide 4%

Micronized

Josie Maran Argan Daily Moisturizer Mineral Protect & Perfect

Titanium dioxide 5.9%; Zinc Oxide 9.4%

Micronized

Murad City Skin Age Defense

Titanium dioxide 2.7%; Zinc Oxide 10%

Micronized

Annmarie Skincare

Zinc oxide 15%

Non-micronized zinc oxide

Badger Unscented Tinted Sunscreen

Zinc oxide 18.75%

Non-micronized zinc oxide

Kabana Green Screen Tinted

Zinc Oxide 25%

Non-micronized zinc oxide

Avasol

Titanium Dioxide 6%; Zinc Oxide 22.5%

Non-micronized zinc oxide

Rubber Ducky Naturally Tinted Stick

Titanium Dioxide 7%; Zinc Oxide 8.5%

Non-micronized zinc oxide

Marie Varonique Organics tinted

Zinc Oxide 20%

Non-micronized zinc oxide

Practical Tips

  • Physical sunscreens include titanium dioxide and zinc oxide. These sunscreens provide the broadest coverage of sun protection, but leave a whiter cast on skin.
  • Micronized titanium dioxide and zinc oxide formulations are less opaque, making them more cosmetically appealing, however they are less effective at blocking longer wavelengths such as UVA and visible light.
  • Iron oxide can be added to zinc and titanium sunscreens to decrease the appearance of the “white cast” on the skin, and can increase the range of coverage against UVA and visible light.
  • Sunscreens with iron oxide can help prevent recurrence and reduce pigmentation in patients with melasma.
* This Website is for general skin beauty, wellness, and health information only. This Website is not to be used as a substitute for medical advice, diagnosis or treatment of any health condition or problem. The information provided on this Website should never be used to disregard, delay, or refuse treatment or advice from a physician or a qualified health provider.

References

References

  1. Pinnell, S.R., et al., Microfine zinc oxide is a superior sunscreen ingredient to microfine titanium dioxide. Dermatol Surg, 2000. 26(4): p. 309-14.
  2. Lowe, N.J., An overview of ultraviolet radiation, sunscreens, and photo-induced dermatoses. Dermatol Clin, 2006. 24(1): p. 9-17.
  3. American Academy of Dermatology. Sunscreen FAQs. April 30, 2019]; Available from: https://www.aad.org/media/stats/prevention-and-care/sunscreen-faqs.
  4. Liebel, F., et al., Irradiation of skin with visible light induces reactive oxygen species and matrix-degrading enzymes. J Invest Dermatol, 2012. 132(7): p. 1901-7.
  5. Randhawa, M., et al., Visible Light Induces Melanogenesis in Human Skin through a Photoadaptive Response. PLoS One, 2015. 10(6): p. e0130949.
  6. Mahmoud, B.H., et al., Impact of long-wavelength UVA and visible light on melanocompetent skin. J Invest Dermatol, 2010. 130(8): p. 2092-7.
  7. Duteil, L., et al., Differences in visible light-induced pigmentation according to wavelengths: a clinical and histological study in comparison with UVB exposure. Pigment Cell Melanoma Res, 2014. 27(5): p. 822-6.
  8. Regazzetti, C., et al., Melanocytes Sense Blue Light and Regulate Pigmentation through Opsin-3. J Invest Dermatol, 2018. 138(1): p. 171-178.
  9. Heurung, A.R., S.I. Raju, and E.M. Warshaw, Adverse reactions to sunscreen agents: epidemiology, responsible irritants and allergens, clinical characteristics, and management. Dermatitis, 2014. 25(6): p. 289-326.
  10. Cross, S.E., et al., Human skin penetration of sunscreen nanoparticles: in-vitro assessment of a novel micronized zinc oxide formulation. Skin Pharmacol Physiol, 2007. 20(3): p. 148-54.
  11. Filipe, P., et al., Stratum corneum is an effective barrier to TiO2 and ZnO nanoparticle percutaneous absorption. Skin Pharmacol Physiol, 2009. 22(5): p. 266-75.
  12. Kaye, E.T., et al., Efficiency of opaque photoprotective agents in the visible light range. Arch Dermatol, 1991. 127(3): p. 351-5.
  13. Kullavanijaya, P. and H.W. Lim, Photoprotection. J Am Acad Dermatol, 2005. 52(6): p. 937-58; quiz 959-62.
  14. Castanedo-Cazares, J.P., et al., Near-visible light and UV photoprotection in the treatment of melasma: a double-blind randomized trial. Photodermatol Photoimmunol Photomed, 2014. 30(1): p. 35-42.
  15. Schalka, S., New data on hyperpigmentation disorders. J Eur Acad Dermatol Venereol, 2017. 31 Suppl 5: p. 18-21.
  16. Boukari, F., et al., Prevention of melasma relapses with sunscreen combining protection against UV and short wavelengths of visible light: a prospective randomized comparative trial. J Am Acad Dermatol, 2015. 72(1): p. 189-90 e1.