Red Light Therapy for Fertility: Why Spotting or Cycle Changes Can Happen

If you’ve recently started red light therapy for fertility and noticed your cycle looks a little different, or you’ve experienced unexpected spotting you’re not alone. This is one of the most common questions I get. Based on the current evidence of minimal adverse events in the research - this isn’t thought to be a cause for concern

Changes in your cycle don’t automatically mean something is wrong. In fact, these changes can actually be a sign that your body is responding to the therapy.

1. Your Uterus Is Getting Better Blood Flow

Red and near-infrared light improve blood circulation by triggering nitric oxide release, which relaxes blood vessels. Translation? Your uterus and endometrial lining get more oxygen and nutrients. When blood flow increases, your uterine lining may remodel or shed a bit differently. That can look like lighter bleeding, heavier bleeding, or spotting between periods, especially in the first few cycles. Think of it as your lining “re-setting” in response to your improved circulation.

2. Inflammation Is Calming Down

Photobiomodulation (PBM) doesn’t just help mitochondria (the little powerhouses in your cells). It also reduces pro-inflammatory chemicals like IL-1β and TNF-α. When inflammation in your pelvic area decreases, prostaglandin levels and endometrial shedding patterns can shift. For some women, that means cramps feel different. For others, it means their flow changes for a cycle or two while their body adjusts.

3. Your Endometrium Is Remodeling

This is one of the most exciting areas of research. Studies using red light in fertility settings show that PBM can boost endometrial cell growth and gene expression, basically helping the lining become thicker and more receptive (with the right device, power and wavelengths).

That kind of cellular activity is exactly what you want for implantation. But as your endometrium responds to this “remodeling,” you might notice temporary spotting along the way.

4. Hormones & Melatonin Are Shifting Too

Here’s a piece most people don’t connect: light directly influences melatonin, and melatonin plays a big role in reproductive health. There are melatonin receptors in your ovaries and uterus, and melatonin levels naturally rise in the luteal phase of your cycle. Women who improve their evening light habits alongside PBM (think: fewer bright screens at night, darker bedrooms) often notice hormone-related shifts in their cycles. For some, that feels like a change at first, but it’s actually a positive sign of your circadian rhythm getting back on track. (Don’t use your devices late at night when your body is expecting dim, low level lighting).

When to Simply Watch & When to Check In

Most of the time, spotting or cycle changes are short-term and resolve within a few cycles. Keep a simple log of your sessions, cycle days, and any spotting. Patterns can give us powerful information about how our body is responding to lifestyle changes.

But you’ll definitely want to talk with your provider if you notice:

• Heavy bleeding (soaking through a pad or tampon an hour for more than 2 hours).

• Bleeding lasting more than 7–8 days.

• Cycles shorter than 21 days or longer than 45 days.

• Severe pelvic pain, fever, or unusual discharge.

• Any bleeding when you’ve had a positive pregnancy test.

Spotting or cycle shifts after starting red light therapy are often just part of your body adjusting to better blood flow, reduced inflammation, and healthier hormonal signaling. These changes are usually temporary, and the research so far supports both the safety and fertility benefits of PBM.

So if your cycle looks a little different right now, don’t panic. Instead, see it as your body doing the important work of recalibration.

Has this happened to you? I’d love to hear about your experiences.

Having a hard time choosing a device? Compare red light therapy devices here and learn about ‘stacking’ red light devices for optimal benefits.

Resources:

Chen, F. et al. (2020). Photobiomodulation pretreatment improves endometrial preparation in women with recurrent implantation failure. [He-Ne 633 nm study].

Zhevago, N.A., & Samoilova, K.A. (2006). Pro- and anti-inflammatory cytokine balance after red light therapy.

Phypers, R., Berisha-Muharremi, V., & Hanna, R. (2024). The Efficacy of Multiwavelength Red and Near-Infrared Transdermal Photobiomodulation Light Therapy in Enhancing Female Fertility Outcomes and Improving Reproductive Health: A Prospective Case Series with 9-Month Follow-Up. Journal of Clinical Medicine, 13(23), 7101. doi:10.3390/jcm13237101.

https://www.sciencedirect.com/science/article/abs/pii/S0891584917307578