Nanoparticles in Cosmetics: Do They Actually Penetrate Skin?

The Short Answer

According to a comprehensive 2021 review by Ferraris et al.:

"Poor dermal permeation of nanomaterials generally limits their potential toxic effects; most nanoparticles remain confined to the stratum corneum and do not reach viable epidermal cells."

- Ferraris 2021, Pharmaceutics

Only nanoparticles smaller than 10nm showed limited penetration to the viable epidermis - and even then, they didn't reach the dermis or systemic circulation.

Where Nanoparticles Actually Go

When you apply a sunscreen or cosmetic with nano-TiO₂ or nano-ZnO, the particles:

Accumulate on the external surface of the stratum corneum
Collect in skin furrows and wrinkles
Deposit in follicle openings (hair follicles, sweat glands)
Do NOT penetrate through intact stratum corneum to viable cells

This is why nano-sunscreens work: the particles stay on the skin surface where they can block UV rays, without absorbing into your body.

The Size Threshold

Penetration by Particle Size

Particle Size	Penetration
> 100nm	Confined to stratum corneum surface
10-100nm	Stratum corneum only
< 10nm	Limited penetration to viable epidermis (not dermis)

Source: Ferraris 2021. Cosmetic nano-TiO₂ and ZnO are typically 20-100nm.

Cosmetic-grade nano-titanium dioxide and zinc oxide typically range from 20-100nm - well above the threshold for deeper penetration.

Silver Nanoparticles: A Different Story

Silver nanoparticles (used in some antimicrobial products) show slightly more penetration according to Missaoui et al. (2018):

25-49nm silver nanoparticles penetrated human stratum corneum
Intact skin: median 0.46 ng/cm²
Damaged skin: 2.32 ng/cm² (5x more)
Reached outermost epidermis layers but not systemic circulation

Key point: damaged skin allows more penetration. This is why nanoparticle safety assessments consider compromised skin barriers.

The ZnO + TiO₂ Interaction

A fascinating 2022 study by Liang et al. found something unexpected: when you combine zinc oxide and titanium dioxide nanoparticles (as many sunscreens do), they're actually safer together than separately.

Antagonistic Effects (Liang 2022)

ZnO alone (20 μg/mL) caused significant cytotoxicity and DNA damage in keratinocytes
Adding TiO₂ significantly reduced ZnO-induced toxicity
Mechanism 1: Increased particle aggregation reduces cellular uptake
Mechanism 2: Competition for cell entry pathways (caveolae-mediated endocytosis)
TiO₂ restricted intracellular Zn²⁺ ion release from ZnO particles

This is why combination sunscreens with both filters may actually have a better safety profile than single-filter products.

Surface Coatings Matter

One of the main concerns with nano-TiO₂ is photocatalytic activity - the particles can generate reactive oxygen species (ROS) when exposed to UV light. But this is largely solved by surface coatings:

Silica coatings suppress ROS generation
Alumina coatings provide similar protection
Coated nanoparticles show significantly improved safety profiles
Most cosmetic-grade nano-TiO₂/ZnO are coated

When you see "titanium dioxide [nano]" in an EU ingredient list, it's almost certainly a coated, cosmetic-grade material - not bare reactive particles.

EU Regulatory Requirements

The EU has specific requirements for nanomaterials in cosmetics under Regulation 1223/2009:

EU Nano Regulations

[nano] labeling: Required in ingredient list when particles are <100nm
Pre-market notification: 6 months before product launch
SCCS safety assessment: Mandatory for colorants, preservatives, UV filters
Maximum concentration: 25% for TiO₂ and ZnO in sunscreens
Spray prohibition: Not permitted in aerosolized products (inhalation concern)

The Inhalation Caveat

Here's an important distinction: while dermal application of nanoparticles is generally safe, inhalation is a different matter.

This is why:

Nano-TiO₂ is prohibited in spray sunscreens in the EU
Powder products with nanoparticles require careful formulation
The lungs have different absorption characteristics than skin

The dermal safety data doesn't apply to inhaled particles. Stick to lotions and creams if you want to avoid any nano-related concerns entirely.

Synthetic Skin Validation

A 2023 review by Saweres-Argüelles et al. provided reassuring data: synthetic skin models showed similar penetration profiles to human/animal skin for nanoparticles.

This means:

We can study nanoparticle penetration without animal testing
The alternative testing methods are validated and reliable
Results confirm: minimal penetration to viable epidermis or dermis
No major toxicological effects observed in actual skin studies

Practical Takeaways

Evidence-Based Guidance

Nano-sunscreens are safe on intact skin - particles stay in the stratum corneum where they belong.
Avoid nanoparticles on damaged/broken skin - compromised barriers allow more penetration.
Combination ZnO+TiO₂ may be safer than single filters - antagonistic effects reduce individual toxicity.
Skip nano spray sunscreens - inhalation is a legitimate concern; lotions and creams are fine.
Look for [nano] in EU products - required labeling tells you when nanoparticles are present.

The Bottom Line

The nanoparticle fear is largely unfounded for dermal cosmetic use. Decades of penetration studies consistently show that particles above 10nm don't reach viable skin cells, let alone systemic circulation.

Nano-TiO₂ and nano-ZnO provide excellent UV protection with cosmetic elegance (no white cast) and minimal absorption. The key caveats are avoiding damaged skin application and steering clear of spray formulations.

References

Ferraris C, et al. (2021). Nanosystems in Cosmetic Products: A Brief Overview of Functional, Market, Regulatory and Safety Concerns. Pharmaceutics. DOI: 10.3390/pharmaceutics13091408
Liang Y, et al. (2022). Antagonistic Skin Toxicity of Co-Exposure to Physical Sunscreen Ingredients Zinc Oxide and Titanium Dioxide Nanoparticles. Nanomaterials. DOI: 10.3390/nano12162769
Missaoui WN, Arnold RD, Cummings BS (2018). Toxicological status of nanoparticles: What we know and what we don't know. Chemico-Biological Interactions. DOI: 10.1016/j.cbi.2018.07.015
Saweres-Argüelles C, et al. (2023). Skin absorption of inorganic nanoparticles and their toxicity: A review. European Journal of Pharmaceutics and Biopharmaceutics. DOI: 10.1016/j.ejpb.2022.12.010
Maghraby YR, et al. (2024). Overview of Nanocosmetics with Emphasis on those Incorporating Natural Extracts. ACS Omega. DOI: 10.1021/acsomega.4c00062