# The Impact of Immunomodulation during the Luteal Phase: Effects on Infection, Vaccinations, and Behaviours >[!example] 17 June 2023 #blog Immunomodulation means a change in the body's immune system. Something which occurs during the Luteal Phase, the two weeks before our period. Immunomodulation occurs due to the hormone progesterone [[The Menstrual Cycle Basics|that the body produces]] due to ovulation. But this is not just *any* change to the immune system. Progesterone actually *suppresses* it. It causes a down-regulation. Why? Our immune system will usually detect and attack 'foreign entities'. It's what it's designed to do - protect us from anything that isn't 'self'. But if a baby is going to be made, we need to ensure that our body doesn't attack the 'paternal genetic material'.[^1] So the body suppresses the immune system after ovulation. Reducing the chance that the mother's immune system attacks the (half-foreign) fertilised egg (should that happen). Even if we haven't conceived during ovulation, our body doesn't know that. Hence it will act as if it has during the luteal phase, the second half of our cycle. So why does this matter? Three reasons: ### 1. Suppression of the immune system comes at a cost During this time, we have an increased vulnerability to infection. In a nutshell: a lower immune response = a higher chance of infection. It also means that chronic infections may also worsen during this time. ### 2. Vaccinations may not work as well If we have a vaccination when our immune system is suppressed, the response may be 'attenuated' or weakened. So it may be better for us to book a vaccination during the follicular phase. It's a thought! ### 3. It's not just our physiology that changes Many of us develop compensatory behaviours to decrease the likelihood of infection. After all, we have a reduced immune response. We need to protect ourselves somehow, right? Basically, we become grossed out and disgusted by, well, anything gross and disgusting. Which then leads us to either *leave* that gross and disgusting place. Or clean like a mother (pun intended). And honestly, it doesn't need to be entirely gross and disgusting. It may be that we notice these things much more right now. Mine is crumbs. And dog hairs. Stuff that wouldn't bother me much in the first half of my cycle now has me going crazy! So in the luteal phase, we're more likely to clean and scrub and tidy. 'Nesting' if you like. Doing everything we can to protect our body (and potential baby) from infection. Well, either that, or we're nagging at the rest of the family for not pulling their weight. Either way - how freakin' awesome is the body? The thing is, we may not even realise this happens. Not until we [[The Beginners Guide to Menstrual Cycle Tracking|start paying attention to our cycle]], that is. **Note:** OCD and trichotillomania symptoms also increase during this time. ## Sources %%[[(Fleischman and Fessler, 2011)]]%%Fleischman, D.S. and Fessler, D.M. (2011) ‘Progesterone’s effects on the psychology of disease avoidance: support for the compensatory behavioral prophylaxis hypothesis.’, _Horm Behav_, 59(2), pp. 271–5. Available at: [https://doi.org/10.1016/j.yhbeh.2010.11.014](https://doi.org/10.1016/j.yhbeh.2010.11.014). %%[[(Wilder, 1998)]]%%Wilder, R.L. (1998) ‘Hormones, pregnancy, and autoimmune diseases.’, _Ann N Y Acad Sci_, 840, pp. 45–50. Available at: [https://doi.org/10.1111/j.1749-6632.1998.tb09547.x](https://doi.org/10.1111/j.1749-6632.1998.tb09547.x). %%[[(Zelazniewicz et al., 2016)]]%%Żelaźniewicz, A. _et al._ (2016) ‘The progesterone level, leukocyte count and disgust sensitivity across the menstrual cycle.’, _Physiol Behav_, 161, pp. 60–65. Available at: [https://doi.org/10.1016/j.physbeh.2016.04.002](https://doi.org/10.1016/j.physbeh.2016.04.002). [^1]: Remember, our cycle is all about conception whether we like it or not.