How red light therapy supports reproductive health - it’s not just about ATP (energy). It plays a key role in reducing cellular stress.
When we hear the word "stress," we tend to think about deadlines, sleepless nights or the emotional strain of trying to conceive.
We rarely picture an egg cell.
But cells experience their own kind of stress. They can face damage to their internal machinery, an excess of reactive chemicals or ongoing chronic inflammatory signals from their surroundings. When those challenges become greater than the cell's ability to manage them, its normal work becomes harder. In an egg, that can affect the delicate processes involved in maturation and early development.
And as it turns out, the stress response itself - the body's fight-or-flight wiring runs right through the ovary, in ways scientists are only beginning to map. This isn’t surprising. The body will always prioritize survival over reproduction. Even when that ‘survival’ mode is associated with mental stress and negative self talk - not an actual threat to our survival. Thoughts are not facts - noticing your thoughts and choosing where you put your focus will impact your stress response.
This is not a suggestion that you need to "relax" to improve your fertility. As we'll see, the evidence on emotional stress and conception is more reassuring than most people think (coming soon). But the biology of stress, in the cellular sense, is real and measurable.
Research co-authored by reproductive physiologist Alison Ermisch, PhD, offers a fascinating window into how egg cells handle these challenges. It also helps explain why scientists are interested in red light therapy for fertility, and why the story goes far beyond giving mitochondria an energy boost.
In a Nutshell
· Egg cells can experience biological stress from age-related changes, inflammation and oxidative chemistry - and that stress can interfere with maturation and early development.
· Oxidative stress is a balance problem, not a simple case of "free radicals bad, antioxidants good." A cell needs reactive molecules as signals, kept under control.
· More energy (ATP) does not automatically mean better egg quality. Spindle abnormalities in Ermisch's research did not correlate with the eggs' ATP content.
· Implantation is a signalling conversation: Toll-like receptors and the anti-stick molecule MUC1 must be switched on and off at exactly the right times for an embryo to attach.
· The egg's whole ecosystem matters: UCSF researchers found stress nerves, support cells and scarring (fibrosis) in the ovary change with age, shaping the environment eggs mature in.
· Red light therapy (photobiomodulation) can influence redox balance, cellular signalling and even TLR4-driven inflammation in laboratory research - promising targets for fertility, though human evidence is still emerging.
What does a stressed egg cell actually look like?
Imagine a small, highly organised workshop or a production line.
Energy is being produced. Materials are moving between workstations. Instructions are being stored and read. A maintenance team on the production line is checking for damage, while messages arrive from neighboring cells.
An egg carries out versions of all these activities. Its mitochondria help supply energy and participate in signalling. Its antioxidant systems manage reactive molecules. Its surrounding support cells help create the conditions in which it matures. Meanwhile, structures inside the egg organise its chromosomes for division.
Cellular stress develops when something disrupts that organisation.
Possible sources include:
· Age-related changes in mitochondria and cellular maintenance.
· Persistent inflammation in the surrounding ovarian environment.
· Metabolic disturbances, including changes associated with obesity and insulin resistance.
· Exposure to some pollutants and toxic substances.
· Laboratory conditions that challenge eggs during collection and maturation for IVF
These are interacting biological influences, not a checklist of things someone has done wrong. Ovarian aging and fertility are complex, and no single stress pathway explains them all.
Oxidative stress: when useful chemistry becomes too much
Every day, cells use oxygen as part of the chemistry that keeps them alive. That activity also produces reactive oxygen species, often shortened to ROS. These are oxygen-containing molecules that readily react with other molecules.
You can think of them as tiny chemical sparks.
A few sparks can carry useful messages. Too many, in the wrong place or for too long, can damage proteins, fats in cell membranes and DNA. Cells therefore have antioxidant systems that keep these reactions under control.
Oxidative stress happens when that balance is disturbed - because reactive molecules are being produced too quickly, protective systems are struggling, or both.
In an egg cell, oxidative stress can interfere with mitochondria and the spindle, the structure that helps organise chromosomes during division. It can also affect the egg's ability to support development after fertilisation.
What did Ermisch's research reveal?
In a 2019 study, Pasquariello, Ermisch and colleagues found that older mouse eggs had altered mitochondrial function and distribution, increased reactive oxygen species and more spindle abnormalities. Antioxidant treatment during laboratory maturation improved several of these cellular features.
One particularly interesting finding was that spindle abnormalities did not correlate with the eggs' ATP content. ATP is the molecule cells use to transfer energy.
In other words, checking the fuel supply did not tell the whole story about how well the machinery was working.
That is an important insight for understanding egg quality: the goal is not simply more energy, but a cell that can use energy while protecting its structures and carrying out its tasks in the right order.
What is redox? The cell's chemical balancing system
"Redox" sounds complicated, but it describes something happening constantly inside you.
The word combines reduction and oxidation: paired chemical reactions in which electrons — the tiny charged particles involved in chemical bonds — move between molecules. Cells use these reactions to release energy, manage reactive substances and communicate.
Think of redox as the cell's balance between useful chemical activity and protective control.
Redox balance does not mean removing every reactive molecule. It means keeping those molecules at levels and in locations where they can do useful work without overwhelming the cell.
That is why "free radicals are bad, antioxidants are good" isn’t a full explanation. The cell needs both signals and safeguards.
Why redox matters to red light therapy
Photobiomodulation - the scientific term for low-level light therapy - can influence this chemical balance.
In experimental research, red and near-infrared light can produce a small, temporary increase in reactive oxygen species that acts as a signal. In some stressed cells, PBM can instead help reduce excessive oxidative stress. The response depends on the cell's starting condition and the light exposure used.
This is more interesting than simply "charging a battery."
Light can influence the messages that help cells respond to their circumstances.
Cellular signalling: how a cell knows what to do next
Cells don’t have thoughts, but they constantly receive and respond to information.
A hormone arriving at a cell, a change in calcium inside it or a small shift in reactive oxygen molecules can all act as signals. These signals start chains of chemical events that change what the cell does.
Imagine someone pressing a doorbell.
The button does not open the door itself. It starts a sequence: a signal travels, someone responds and an action follows.
Cellular signalling works in a similar way. A small initial event can lead to changes in enzyme activity, protective responses, inflammation or the use of genetic instructions.
This is one reason mitochondria deserve more attention than the familiar "powerhouse of the cell" description suggests. They help generate energy, but they also participate in the signalling that coordinates cellular activity.
For PBM, that means a light-induced change in mitochondrial chemistry may have consequences beyond ATP production, including changes in redox, calcium and inflammatory signalling.
TLRs and MUC1: the signalling conversation of implantation
One of Ermisch's studies focused on a molecule called TLR4, short for Toll-like receptor 4 - a receptor that acts as a molecular detector, triggering inflammatory signalling when the immune system senses danger.
Think of it as part of a biological alarm system. An alarm is useful when there is a threat, but persistent inflammatory activity changes the environment in which cells are trying to work.
In her mouse study, a high-fat/high-sugar diet was associated with increased ovarian inflammation and reduced blastocyst development — but only in mice with normal TLR4 signalling, not in mice whose TLR4 response was impaired. The affected eggs also contained altered amounts of stored developmental messages.
But TLR4 is only one member of the family, and the reproductive tract uses these receptors with remarkable timing.
The human endometrium expresses Toll-like receptors 1 through 10, with several peaking in the secretory phase — the part of the cycle that ends with the implantation window. A recent review describes how TLR2 and TLR4 play opposite roles: TLR2-triggered, precisely controlled inflammation is part of normal reproductive housekeeping, helping clear the uterus after sperm arrive, while TLR4-driven inflammation — the same pathway from Ermisch's study, tips into tissue damage when it becomes excessive. Interestingly, TLR4 expression is dialled down during the luteal phase, exactly when the uterus must become receptive for an embryo to implant.
Then there is MUC1 - perhaps the most elegant piece of the implantation story.
MUC1 is a large, sugary molecule that coats the surface of the uterine lining. It is deliberately anti-adhesive: a non-stick coating that stops anything from attaching to the endometrium at the wrong time.
Here is the remarkable part. In humans, MUC1 is actually most abundant during the receptive phase. But when a healthy embryo makes contact, it sends signals that trigger the local removal of MUC1 - only at the precise spot where the embryo stands. The non-stick coating is lifted, like a single pane being opened in a sealed window, and attachment can begin there and only there.
Implantation, in other words, is not one cell sticking to another. It is a timed conversation between embryo and uterus, involving molecular alarms, anti-stick barriers and signalling that must switch on and off in the right sequence.
(I’ve written about red light therapy and implantation timing in another article) - https://blog.tracydonegan.org/blog/red-light-therapy-and-implantation-success
The egg has an instruction library - and timing matters
An egg prepares for early development by storing messenger RNA, or mRNA.
These molecules are working copies of genetic instructions. They tell the cell which proteins to make. As an egg approaches maturation, its ability to produce new messages becomes restricted, so it must carefully manage the instructions already stored inside it.
Imagine a library prepared for a period when no new books can arrive.
Success depends on more than having plenty of books. The right instructions must be available, read at the right time and put away or cleared when no longer needed.
In Ermisch's inflammation study, several maternal-effect transcripts - messages relevant to early development - were more abundant in the affected eggs, even though embryo development was poorer.
More messages did not mean better performance.
The researchers considered changes in the way the eggs used or cleared those messages as possible explanations.
This adds an important layer to how we think about cellular stress: it may affect not only the egg's energy supply, but also the organisation of its developmental programme.
The egg's support team matters too
Eggs do not mature in isolation.
They develop inside follicles, surrounded by cells that help support and regulate their growth. Cumulus cells, which sit immediately around the egg, are part of this close communication network.
In another study co-authored by Ermisch, researchers used a carefully designed laboratory medium to support this egg–support-cell relationship before maturation. A two-hour preparation period improved subsequent embryo development, whereas a much longer preparation period did not produce the same benefit.
That finding highlights something easily missed in fertility conversations: good cellular function depends on timing and teamwork, not just stimulation.
The ovarian ecosystem: stress nerves and scarring
In October 2025, researchers at UC San Francisco and the Chan Zuckerberg Biohub published a landmark study in Science that changed how scientists think about the ovary. I covered this and red light therapy in an earlier article. https://blog.tracydonegan.org/blog/the-newly-discovered-ecosystem-of-ovaries-and-how-red-light-therapy-may-help-it-thrive
Using a new 3D imaging technique that made whole ovaries transparent instead of slicing them into thin sections, the team led by Diana Laird, PhD, mapped ovaries from mice and humans in unprecedented detail. Three discoveries stand out.
Eggs live in neighborhoods. Rather than being scattered evenly, eggs cluster in "pockets," and the density of eggs within these pockets declines with age. The local environment around an egg may influence how long it lasts and how well it matures.
The ovary is wired for stress. Sympathetic nerves - the same nerves behind the fight-or-flight response form dense networks throughout the ovary, and those networks become even denser with age. When researchers removed these nerves in mice, the animals had more eggs in reserve but fewer that matured, suggesting the nerves help decide when eggs begin to grow.
The ovary scars early. Fibroblasts, the cells that provide structural support, change with age in ways that trigger inflammation and scarring, fibrosis in the ovaries of women in their 50s, years earlier than comparable scarring in organs like the lungs or liver.
So does emotional stress affect your eggs?
This is where the story deserves both honesty and reassurance.
The stress-response wiring is physically present in the ovary, and a 2024 mouse study found that chronic, sustained stress can drive ovarian fibrosis and impair fertility, partly through oxidative stress. So the biological link between long-term stress and the ovarian environment is a genuine and active research area.
But the popular idea that worrying will stop you conceiving is not supported. UCSF's own researchers have found that women reporting psychological distress before IVF were just as likely to become pregnant as those who felt stress-free - if anything, the distress tended to follow unsuccessful treatment rather than cause it.
The picture that emerges is neither "stress doesn't matter" nor "just relax." It is that the ovarian environment - its nerves, its support cells, its inflammation and scarring is built over years, not ruined or rescued by a single stressful week.
Where red light therapy fits into this picture
The connection between Ermisch's work and PBM is not that she demonstrated a light treatment for eggs. It is that her research helps identify what deserves protection: mitochondrial function, redox balance, communication with support cells and the orderly use of developmental instructions.
The implantation research widens that target further. If TLR-driven inflammation and MUC1 removal must be timed just so, then therapies that modulate inflammatory signalling become relevant questions, not afterthoughts.
Here PBM research offers something unusually direct. In laboratory studies using human cell cultures, infrared light exposure significantly reduced inflammation triggered through the TLR4 signalling pathway - the very pathway implicated in Ermisch's ovarian inflammation study - while leaving healthy cells largely unaffected. Similar TLR4-dampening effects have been reported in animal models of inflammation, alongside reductions in NF-κB, the molecular switch downstream of TLR activation.
Laboratory research has found that 635 nm light increases the proliferation and functional activity of cultured human endometrial cells, the very cells whose receptivity matters for implantation. And in 2024, a small randomised trial of women with recurrent implantation failure treated with 850 nm transabdominal laser before frozen embryo transfer saw higher biochemical (46.7% vs 33.3%) and clinical pregnancy (33.3% vs 20%) rates.
Add the 2024 mouse study in which 650 nm light improved mitochondrial function, oxidative stress, inflammation and new blood-vessel growth in aged ovaries, and the overlap gives this research its promise: rather than merely increasing cellular fuel, light therapy may help create the conditions in which reproductive cells and tissues function more effectively.
Frequently asked questions
Can a cell really get stressed?
Yes. Cellular stress refers to biological challenges - reactive chemicals, damaged proteins, poor energy production or inflammatory signals - that push a cell's maintenance systems beyond what they can comfortably manage. It is a physical, measurable process, not an emotional one.
What is redox?
Redox is the cell's balance of chemical reactions that move electrons between molecules. Cells need these reactions for energy and communication, but they also need antioxidant systems to keep them controlled. Oxidative stress means that balance has tipped too far in one direction.
Does stress affect egg quality?
The honest answer is nuanced. A single stressful week or an anxious IVF cycle does not appear to reduce your chances - UCSF studies found psychological distress before treatment did not change pregnancy rates. But the biology of long-term stress is real: the ovary contains fight-or-flight nerves that change with age, and in mice, chronic sustained stress has been shown to promote ovarian scarring and oxidative damage. Researchers think of the ovarian environment as something built over years, which is why it is an active target for therapies - including light therapy that support tissue health.
What is a spindle in an egg cell?
A spindle is a temporary structure inside a cell that helps organise and separate its chromosomes during cell division. Chromosomes are packages of DNA containing genetic instructions.
Think of the spindle as a carefully coordinated set of microscopic ropes. These "ropes," called microtubules, attach to chromosomes, line them up and move them towards opposite sides of the cell.
An egg must go through a special type of cell division called meiosis. This reduces its chromosome number so that, when egg and sperm combine, the resulting embryo receives the correct amount of genetic material. The spindle acts as the chromosome-sorting machinery, helping ensure the egg keeps the correct set while the extra genetic material is moved into a tiny neighbouring cell called a polar body.
If the spindle forms incorrectly or fails to separate chromosomes accurately, an egg can end up with too many or too few chromosomes. This is called aneuploidy, and it is a major reason egg quality involves more than having enough energy. Human-egg research shows that spindle instability and age-related changes in chromosome attachment contribute to these sorting errors.
Want to explore light therapy as part of your fertility journey?
If you're trying to conceive, you may be wondering whether low-level laser therapy deserves a place in your plan. The research into how egg cells manage stress, inflammation and their developmental instructions is still emerging — and that's exactly why an evidence-informed approach matters.
The Solasta low-level laser is the device I use in my own women's-health protocols. It combines 650 nm red and 808 nm near-infrared light in a handheld unit designed for simple, timed home use - no guesswork about settings or session length.
If you'd like to understand what the evidence does and doesn't support, and whether light therapy fits your circumstances, I'd love to help you work through it.
[Explore Solasta and my fertility protocol guidance at TracyDonegan.org]
So - energy is crucial for a healthy reproductive system…it’s crucial for health in every system of the body. But PBM is doing so much more than boosting cellular energy. The positive cascade is having a powerful effect on every aspect of the folllicular environment.
Tracy
References
1. Pasquariello F, Ermisch AF, et al. Alterations in oocyte mitochondrial number and function are related to spindle defects and occur with maternal aging in mice and humans. Biology of Reproduction. 2019;100(4):971–981. https://doi.org/10.1093/biolre/ioy248
2. Ermisch AF, et al. Ovarian inflammation mediated by Toll-like receptor 4 increased transcripts of maternal effect genes and decreased embryo development. Biology of Reproduction. 2023;108(3):423–436. https://doi.org/10.1093/biolre/ioac212
3. Ermisch AF, Wood JR. Regulation of Oocyte mRNA Metabolism: A Key Determinant of Oocyte Developmental Competence. In: Molecular Mechanisms Determining Mammalian Oocyte Quality. Springer; 2024:23–46. https://doi.org/10.1007/978-3-031-55163-5_2
4. Huang YY, Sharma SK, Carroll J, Hamblin MR. Proposed Mechanisms of Photobiomodulation or Low-Level Light Therapy. Biomedical Optics Express. 2017. https://pmc.ncbi.nlm.nih.gov/articles/PMC5215870/
5. He Y, Ye R, Peng Y, et al. Photobiomodulation ameliorates ovarian aging by alleviating oxidative stress and inflammation damage and improving mitochondrial function. Journal of Photochemistry and Photobiology B: Biology. 2024;260:113024. https://doi.org/10.1016/j.jphotobiol.2024.113024
6. Santiquet NW, Greene AF (Ermisch), et al. A pre-in vitro maturation medium containing cumulus oocyte complex ligand-receptor signaling molecules maintains meiotic arrest, supports the cumulus oocyte complex and improves oocyte developmental competence. Molecular Human Reproduction. 2017;23(9):594–606. https://doi.org/10.1093/molehr/gax032
7. Liang J, Liu J, Zhang L, et al. Photobiomodulation—Underlying Mechanism and Clinical Applications. Journal of Clinical Medicine. 2020;9(6):1724. https://pmc.ncbi.nlm.nih.gov/articles/PMC7356229/
8. Chiang G, Heifetz Y, Schuh M, Eggert US. Aneuploidy in human eggs: contributions of the meiotic spindle. Biochemical Society Transactions. 2021;49(1):107–118. https://pmc.ncbi.nlm.nih.gov/articles/PMC7925012/
9. Santiquet NW, et al. Molecular Human Reproduction. 2017. https://doi.org/10.1093/molehr/gax032
10. Gaylord E, et al. (Laird lab). Ovarian aging and the follicular ecosystem study. Science. 2025. https://doi.org/10.1126/science.adx0659 — See also: UCSF News, "Why Does Female Fertility Decline So Fast? The Key Is the Ovary," October 2025. https://www.ucsf.edu/news/2025/10/430841/why-does-female-fertility-decline-so-fast-key-ovary
11. Chronic stress causes ovarian fibrosis to impair female fertility in mice. Biochemical Pharmacology. 2024. https://www.sciencedirect.com/science/article/abs/pii/S0898656824003024
12. University of California San Francisco. "How Much Can We Control Our Own Fertility?" UCSF Magazine. https://magazine.ucsf.edu/can-we-control-our-fertility
13. Kwon JW, et al. Chromosome Segregation in the Oocyte: What Goes Wrong during Aging. International Journal of Molecular Sciences. 2022;23(3):2880. https://pmc.ncbi.nlm.nih.gov/articles/PMC8911062/
14. TLR2 and TLR4 bridge physiological and pathological inflammation in the reproductive system. Cellular and Molecular Life Sciences. 2025. https://pmc.ncbi.nlm.nih.gov/articles/PMC12228841/
15. Meseguer M, et al. MUC1: A multifunctional cell surface component of reproductive tissue epithelia. Reproductive Biology and Endocrinology. 2004;2:4. https://link.springer.com/article/10.1186/1477-7827-2-4 — See also: University of Manchester, "Human endometrial mucin MUC1 is up-regulated by progesterone and down-regulated by the human blastocyst." https://research.manchester.ac.uk/en/publications/human-endometrial-mucin-muc1-is-up-regulated-by-progesterone-and-/
16. Mester E, et al. Therapeutic application of light and electromagnetic fields to reduce inflammation — infrared light suppresses the TLR4-dependent inflammatory response in human cell cultures. Photobiomodulation, Photomedicine, and Laser Surgery. 2021. https://pmc.ncbi.nlm.nih.gov/articles/PMC8096326/ — See also: de Brito AA, et al. Beneficial effects of red LED treatment in experimental acute lung injury. Scientific Reports. 2017. https://pmc.ncbi.nlm.nih.gov/articles/PMC5627274/
17. El Faham SAA, et al. The efficacy of low-level laser therapy in enhancing the proliferation and functional capacity of cultured human endometrial cells. 2018. (As reviewed in: Clinical Applications of Low-Level Laser Therapy in Reproductive Medicine.) https://www.academia.edu/80412775/Clinical_Applications_of_Low_Level_Laser_Therapy_in_Reproductive_Medicine_A_Literature_Review
18. Zare F, et al. Low-Level Laser Therapy for Improvement of In Vitro Fertilization Outcomes in Patients with Recurrent Implantation Failure: A Randomized Clinical Trial. Journal of Lasers in Medical Science. 2024;15:e15. https://pmc.ncbi.nlm.nih.gov/articles/PMC11266823/
