As medical professionals, we typically focus on dosage (the amount of medication, frequency, and duration). However, there’s an additional aspect that is frequently neglected: time. For years, we have understood that the body metabolizes medications differently depending on the time of day. A blood pressure medication or chemotherapy agent can produce significantly different outcomes based on when it is administered. This area, referred to as chronopharmacology, has revolutionized our approach to drug administration. Yet, this concept seldom surfaces in discussions about everyday environmental exposures (what patients come into contact with via food, cosmetics, or the air they breathe).
What if the timing also affects how our bodies absorb, metabolize, and react to chemicals in these routine scenarios? This inquiry lays the groundwork for what I term chrono-exposomics: the investigation of how timing interacts with the body’s internal circadian rhythm to influence risk.
The body keeps track of time
Almost every organ in the body functions on a 24-hour cycle. The skin, our largest organ, becomes more permeable in the evening. The liver, responsible for detoxification, processes chemicals more effectively during daylight hours. Hormone levels fluctuate in tightly coordinated cycles that affect everything from metabolism and mood to reproduction. In essence, the body maintains time; its associated risks do as well. This implies that an exposure at 8 a.m. may not be biologically the same as the same exposure at 8 p.m.
A case in point: nail products
Think about the straightforward action of receiving a manicure. Countless individuals globally use nail products on a regular basis, often without much consideration. However, many of these items contain chemicals known to interfere with hormone signaling, including endocrine disruptors such as phthalates and organophosphate esters. A recent regulation from the European Union prohibited TPO (trimethylbenzoyl diphenylphosphine oxide), a photoinitiator utilized in gel manicures for curing polish under UV lamps. The justification? It was identified as a reproductive toxicant. Nevertheless, beyond TPO, researchers have discovered other chemicals linked to manicures, like triphenyl phosphate (TPHP), in users’ urine just hours after use. In other words, these substances are absorbed rapidly and systemically.
Timing and absorption
If our skin and liver adhere to daily rhythms, it follows that the timing of exposure could affect the amount absorbed and its duration in the body. In the evening, skin permeability and peripheral blood circulation increase, while liver detoxification activity diminishes. In the morning, detoxification enzymes are at their highest levels, and the skin barrier is sturdier. This combination might suggest that an evening manicure could result in a greater internal chemical dosage than one performed earlier in the day. Although this hypothesis has yet to be directly examined, it is a theory worth investigating, especially in light of what we understand about fertility and circadian rhythms.
Why fertility is particularly susceptible
Reproductive health is one of the body’s systems most sensitive to rhythms. Hormonal surges, ovulation, and implantation all rely on precise circadian timing. Disruption of these rhythms can have considerable effects: irregular cycles, reduced egg quality, and impaired hormone signaling. For patients already facing infertility challenges, environmental exposures that interact with circadian disruptions could exacerbate their difficulties. Research on salon staff supports this worry. Studies indicate elevated levels of phthalate and phosphate metabolites among nail technicians, levels associated with diminished ovarian reserve and altered reproductive hormone profiles. However, the potential impact of timing on these exposures has never been examined.
Practical considerations
Until we gather more evidence, minor, informed adjustments can assist patients in minimizing potential risks while maintaining self-care routines:
Choose safer formulations: Select TPO-free or “3-free”/“5-free” polishes, preferably those that comply with EU ingredient regulations.
Schedule morning appointments: Earlier sessions might result in lower absorption rates and faster clearance.
Protect the skin: Avoid contact with the cuticles, utilize gloves for home applications, and apply mineral sunscreen or UV-protective gloves during curing.
Ensure proper ventilation: Open windows or employ fans to reduce inhalation exposure. For frequent users, consider taking “manicure breaks” to facilitate detox recovery.
Looking forward
The next scientific challenge lies in measuring how circadian timing affects chemical absorption and metabolism. Envision a study that contrasts morning versus evening manicures while monitoring chemical metabolites, hormone levels, and sleep patterns. Such research could shed light on how timing influences exposure risk and possibly inform new safety standards for consumer products. Chrono-exposomics, as a concept, connects what we already understand about circadian biology and toxicology. It emphasizes that prevention is not merely about avoiding exposure but also about aligning with the body’s natural rhythms.
The key takeaway
The beauty of this concept is its simplicity: Our biology adheres to a schedule, and so should our choices. For patients dealing with fertility challenges, minor timing adjustments (in sleep, diet, or daily habits) may provide an additional layer of protection and empowerment.
The body keeps track of time. Perhaps our exposures should align with it as well.