Your Makeup Brushes Are Dirtier Than You Think

Makeup brush cleaning is the step almost everyone skips. It is tedious, it is invisible, and nothing appears to go wrong when you neglect it. Yet the microbiology on this is unusually clear, and it is not comfortable reading.

Researchers at Aston University tested donated, in-use cosmetic products and published the results in the Journal of Applied Microbiology. Between 79 and 90 percent carried bacterial contamination. Blending sponges were the worst offenders by a wide margin.

This guide covers what that research actually found. It explains why sponges and brushes behave so differently, and how to build a cleaning habit that holds. It also explains which claims circulating online have no real evidence behind them. Every study cited here is peer-reviewed and named, so you can check the work yourself.

What the Research on Makeup Brush Cleaning Actually Found

Two independent studies, run years apart on different continents, reached remarkably similar conclusions.

The Aston University findings

Bashir and Lambert examined five categories of used cosmetics: lipstick, lip gloss, eyeliner, mascara, and blending sponges. Roughly 79 to 90 percent of everything tested carried bacteria. Most products showed loads between 100 and 1,000 colony-forming units per millilitre.

Blending sponges were different in kind, not just degree. They averaged over one million colony-forming units per millilitre, roughly a thousandfold higher than other products. The reason becomes obvious once you consider how they are used.

Why blending sponges are the worst offender

A sponge is designed to be used damp. Consequently, it stays damp, holds product deep inside its structure, and sits in a warm bathroom. That combination is close to ideal for bacterial growth.

User behaviour compounds the problem considerably. In the Aston study, 93 percent of sponges had never been cleaned. Furthermore, 64 percent had been dropped on the floor and used again anyway.

A separate study reached the same conclusion

Attar and Imam analysed 57 cosmetic brushes and sponges in Jeddah. Their work appeared in the International Journal of Microbiology in 2025. They used 16S rRNA gene sequencing to identify what was growing, a considerably more precise method than culture alone.

Gram-positive bacteria dominated at 81 percent, mostly Staphylococcus and Micrococcus species. Gram-negative Pseudomonas also appeared. Alongside the lab work, a survey of 370 participants found that 44.3 percent rarely cleaned their brushes at all.

What This Means for Your Skin, Honestly

Here is where careful reading matters, because the honest answer is more nuanced than most coverage admits.

What the evidence supports

Some of the organisms found are genuinely opportunistic pathogens. Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa all appeared across these studies. Each is associated with skin infections when it reaches broken skin.

Risk rises meaningfully in specific situations. Applying product near the eyes, over active breakouts, or onto any cut or graze creates an entry point. People who are immunocompromised face higher risk again.

What the evidence does not yet prove

Now the part most articles leave out. The Jeddah study found no statistically significant link between cleaning frequency and reported skin problems. The p-value was 0.698, which is nowhere near significance.

That single finding deserves respect rather than burial. Contamination is thoroughly documented, but a direct causal line from dirty brushes to your breakouts has not been established. Much of what circulates online overstates this considerably.

The sensible reading sits between the two extremes. Your tools demonstrably carry opportunistic pathogens, and cleaning them is quick and free. Meanwhile, nobody should promise that a weekly wash will clear your skin.

A Makeup Brush Cleaning Method That Holds Up

The method matters less than the consistency. Still, a few details genuinely change the outcome.

How Makeup Brush Cleaning Fits the Rest of Your Routine

Tools are one input among several. Here is how this connects to what you already do for your skin.

Your skin already hosts bacteria, and that is fine

Worth keeping perspective here. Your skin naturally carries trillions of microorganisms, and most are protective rather than threatening. As the Belldiva skin microbiome guide explains, the goal was never sterility.

The concern is different in nature. Dirty tools introduce organisms that do not belong on your face, in concentrations your skin never evolved to handle. That is a separate problem from your resident flora.

Barrier health changes the risk calculation

An intact barrier is remarkably good at keeping opportunistic bacteria out. A compromised one is not. As the Belldiva skin barrier repair guide covers, over-exfoliation and harsh cleansing both weaken that defence.

This is why the two habits reinforce each other. Clean tools reduce what lands on your skin, while a healthy barrier handles whatever still gets through. Neither replaces the other.

Common Questions About Makeup Brush Cleaning

Direct answers to what comes up most often, including where the honest answer is simply that nobody knows yet.

Questions about frequency and method

Questions about skin and makeup brush cleaning habits

Sources and research references

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