UVA ray exposure in the newborn and infant in the first year of life & skin vulnerability in pediatric age

Exposure to ultraviolet (UV) radiation constitutes the main environmental factor responsible for cumulative skin damage and photocarcinogenesis. UV radiation reaching the Earth’s surface is predominantly composed of UVA rays (320–400 nm), divided into UVA2 (320–340 nm) and UVA1 (340–400 nm), and UVB rays (290–320 nm).

UVA  represents over 95% of incident ultraviolet radiation and, thanks to its longer wavelength, penetrates deeply into the skin to the papillary and reticular dermis, where it induces oxidative stress, extracellular matrix alterations, immunomodulation and cell damage mediated by the formation of reactive oxygen species (ROS).
UVB, while penetrating mainly the epidermis, exerts a powerful mutagenic effect through the formation of DNA photoproducts, in particular cyclobutane-pyrimidine dimers (CPD) and photoproducts 6-4 pyrimidine-pirimidone.

The combined action of UVA and UVB leads to a progressive accumulation of molecular alterations that constitute the biological substrate of photoaging, photoinduced immunosuppression and skin carcinogenesis.

 

Why newborn skin is more vulnerable to UV rays

In the newborn and infant, during the first year of life, these effects are amplified by the unique characteristics of the skin, which represents an organ still in the development phase from both a structural and functional point of view.

 

A still immature skin barrier

The skin of the full-term newborn quickly completes its adaptation to extrauterine life, but its maturation continues for several months after birth. In the first 12 months of life the epidermis has a lower thickness compared to adulthood, with a thinner stratum corneum, less cohesion between corneocytes and a barrier function still in evolution. Although transepidermal water loss (transepidermal water loss, TEWL) reaches values close to those of adults within the first weeks of life in healthy full-term newborns, the epidermal barrier maintains greater vulnerability toward physical, chemical, and environmental agents, including ultraviolet radiation. Such immaturity is even more marked in preterm infants, in whom the completion of the skin barrier requires significantly longer times.

 

A thinner and less resistant dermis

The dermis also presents distinctive characteristics. The dermal thickness is reduced and the network of collagen and elastic fibers is still in the organization phase. The extracellular matrix is relatively rich in water and glycosaminoglycans, while the connective tissue offers less resistance to mechanical and oxidative insults. Consequently, the greater penetration capacity of UVA radiation into deep tissues can lead to relatively more extensive biological damage compared to adults.

 

An still incomplete natural protection

Skin pigmentation represents a further element of vulnerability. Although the number of melanocytes is substantially comparable to that of adults from birth, their biosynthetic activity is significantly reduced. In the first months of life, melanin production, melanosome maturation and their transfer to keratinocytes are still incomplete, limiting the effectiveness of natural protection against ultraviolet radiation. This reduced photoprotective capacity favors greater susceptibility to oxidative and mutagenic damage induced by sun exposure.

 

Antioxidant defenses and DNA repair in maturation

The antioxidant defense systems are also functionally immature. The activity of enzymes such as superoxide dismutase, catalase and glutathione peroxidase, fundamental in the neutralization of reactive oxygen species, progressively reaches adult levels during the first year of life. At the same time, the DNA repair mechanisms, although present, show lower functional efficiency in the early stages of development, favoring the persistence of molecular damage resulting from exposure to UV rays.

 

A cutaneous immune system still in development

Neonatal skin also presents immunological peculiarities that contribute to increasing its vulnerability. The cutaneous immune system is characterized by a reduced functional competence of Langerhans cells, by a different arrangement of resident lymphocyte populations and by a still immature production of pro- and anti-inflammatory cytokines. This condition determines a greater susceptibility to photoimmunosuppression induced by UV rays, a phenomenon that interferes with immunological surveillance of genetically damaged cells and represents one of the main mechanisms involved in photocarcinogenesis.

 

Greater skin surface area and greater absorption

A further distinctive feature of the first year of life is the high ratio of body surface area to body weight, approximately two to three times higher than in adults. This peculiarity entails a larger exposed skin surface area in relation to body mass and determines, on one hand, a greater vulnerability to environmental agents and, on the other, a potential increase in the percutaneous absorption of topically applied substances. This aspect is particularly relevant in the choice of photoprotective products intended for infants, in which formulations characterized by a high safety profile, minimum systemic bioavailability and low irritative or sensitizing potential must be favored.

 

The role of the skin microbiome

The skin microbiome, a fundamental element of epidermal homeostasis and immune regulation, also undergoes profound modifications during the first year of life. Microbial colonization begins immediately after birth and continues to evolve in the following months, progressively contributing to the maturation of the barrier function and skin immune responses. Ultraviolet radiation-induced alterations in epidermal integrity can interfere with this delicate development process.

 

 

Recommendations for photoprotection in the first six months of life

For these reasons, all major international scientific societies including the American Academy of Pediatrics (AAP, 2022), the American Academy of Dermatology (AAD, 2024) and the Cancer Council Australia (2023), recommend that infants under six months of age should not be directly exposed to sunlight. In this age group, photoprotection must be achieved primarily through behavioral strategies and physical barriers, including staying in the shade, the use of clothing with a high ultraviolet protection factor (UPF), wide-brimmed hats and the use of strollers and prams equipped with hoods or shielding systems made with certified fabrics with high protection against UV rays (UV Protection/UPF). These devices must guarantee effective shielding of ultraviolet radiation without compromising ventilation and air exchange inside the stroller.

It is in fact essential to avoid complete coverage with non-breathable sheets or blankets, a practice that can cause a rapid increase in internal temperature, reduce heat dissipation and significantly increase the risk of hyperthermia and heat stress in the newborn. Hoods designed with breathable technical materials and high UV protection are therefore the preferable solution, as they allow a high photoprotective efficacy to be combined with adequate ventilation and the maintenance of the infant’s thermo-hygrometric comfort.

 

After six months: when to use sunscreen

In infants over six months of age, when sun exposure is unavoidable, topical photoprotection represents a complementary and not a substitute measure for physical strategies. Broad-spectrum products are recommended, effective against both UVB and UVA, with high photostability and a proven safety profile in the pediatric population, preferably formulated with mineral filters or with filter systems specifically developed for sensitive childhood skin.

 

Key message

In light of the unique anatomical, physiological and immunological characteristics of the skin in the first year of life, photoprotection represents a fundamental preventive intervention. Preventing excessive exposure to ultraviolet rays during this developmental window is not only aimed at avoiding the acute effects of radiation, but constitutes a primary prevention strategy aimed at reducing the burden of cumulative actinic damage and the risk of skin cancers in adulthood.
These recommendations, developed by a multidisciplinary panel of experts in pediatric dermatology, are intended to provide evidence-based indications for the appropriate use of photoprotection measures in newborns and infants, integrating the latest knowledge on the physiology of pediatric skin with current evidence on photobiology and pediatric prevention.