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What is the problem?Endocrine disruptors have been defined by the World Health Organisation as “an exogenous substance or mixture that alters functions of the endocrine system and consequently causes adverse health effects in an intact organism, or its progeny or (sub) populations” (World Health Organization, 2017). Endocrine Disruptors’ have been associated with a range of detrimental health effects such as infertility, obesity, diabetes and cancer. A range of ultraviolet filters are used in personal care products. However, concerns have been raised about their potential endocrine disrupting effects and increasingly reported adverse effects to humans and other organisms.  DefinitionsWhat is the endocrine system?The endocrine system is responsible for the control of processes in the body such as cell differentiation and the formation of organs at the development stage along with many tissue and organ functions throughout the adult lifespan (Greenstein and Wood, 2011). Within the body there are numerous glands which make up the endocrine systemwhich are surrounded by an extensive network of capillaries.Figure 1 shows the major glands of the endocrine system (Tes Teach with Blendspace, 2017) and figure 2 explains the functions of these glands. They secrete chemical messengers called hormones which circulate around the body via the blood stream and initiate their actions at distant sites (Bergman et al., 2012).  The receptors of the target organs are molecules consisting of proteins that bind specifically with hormones to stimulate specific physiological changes in the target cell. If there is a change in the amount of a substance e.g. blood hormone levels, the endocrine system will detect this and respond via negative feedback. There are three mechanisms in which the endocrine glands control the release of hormones; humoral stimuli, hormonal stimuli and neural stimuli. Humoral stimuli controls the release of different ions and nutrients in the blood for example when the concertation of the calcium in the blood surrounding the parathyroid gland is low, there is a stimulus to produce parathyroid hormone which in turn increases the calcium levels in the blood. When the calcium concentration is too high the PTH is inhibited. Hormonal stimuli refers to the release of a hormone in response to another hormone. For example, when the hypothalamus produces hormones this stimulates the anterior pituitary gland which releases hormones that regulate hormone production by other endocrine glands. The anterior pituitary gland releases the thyroid stimulating hormone which stimulates the thyroid gland to produce T3 and T4 hormones. When these hormones reach a high they inhibit both the pituitary and the hypothalamus in a negative feedback circle. Neural stimulirefers to the nervous system stimulating the endocrine glands to release hormones. For example, neuronal signalling from the sympathetic nervous system directly stimulates the adrenal medulla to release the hormones epinephrine and norepinephrine (Fowler et al., 2005). Hormones can be classified in accordance to their molecular structure. Steroids are derived from steroid cholesterol and include hormones from the adrenal cortex, testes and ovaries. Polypeptidesinclude hormones from the anterior and posterior pituitary, parathyroid glands and endocrine tissue of the pancreatic gland. Amines are derived from amino acids and eicosanoids are derived from arachidonic acid, a polyunsaturated fatty acid (Johnstone et al., 2014). The endocrine system and the nervous system work closely together with the brain continually sending messages to the endocrine system which in turn receives feedback from the endocrine glands. This relationship is referred to as the neuroendocrine system. Unlike the nervous system, the endocrine system acts in a slower and more precise way which in turn accounts for a high degree of control of bodily functions (Waugh et al.) A table showing the major glands of the endocrine system and their corresponding functionsFigure 1. A diagram showing the major glands of the endocrine system.  Gland FunctionPineal? Situated between the cerebral hemispheres of the brain, this gland secretes melatonin which has an influence on sexual development and sleep cycles? Connects the endocrine system with the nervous system? Transforms nerve signals from the sympathetic system of the peripheral system into hormone signalsPituitary ? Sometimes referred to as the “Master Gland” as it controls other organs/endocrine glands and suppresses/induces hormone production? Divided into two sections: the anterior lobe which regulates the activity of the thyroid, adrenals and reproductive lobes and the posterior lobe which releases antidiuretic hormone, regulating the water balance in the body along with oxytocin which triggers uterus contractions when having a babyHypothalamus ? Made up of a collection of specialised cells and is one of the main links between the endocrine and nervous system? Hypothalamic hormones stimulate or inhibit the secretion of pituitary hormonesThyroid /parathyroid ? Secretes hormones that control metabolism, growth, heart rate, body temperature and calcium levelsThymus ? Main function is to promote development of specific white blood cells- T-lymphocytes? Produces several hormones e.g. thymosin which increases immune responses Pancreas ? Produces insulin and glucagon which help regulate glucose/sugar levels in the blood? Synthesis digestive juices which are composed of enzymes that are released into the bowel prior to food consumption and break down food Adrenal ? Produce mineralocorticoids which help maintain the body’s salt and water levels thus regulating blood pressure? Produce glucocorticoids which is involved in stress response and metabolism ? Produce androgens which are male sex hormones Testes ? Male reproductive glands? Produce androgens (most importantly testosterone)Ovaries ? Female reproductive glands? Produce eggs and secrete the hormone estrogen   What is an ED?The balance of the endocrine system has been shown to be disrupted by chemicals known as endocrine disruptors. Thesechemicals may include UV filters, used as sun blocks in manypersonal care products and every day materials such as sun creams, deodorants, pesticides and plastics (Crowe and Bradshaw, 2010). The World Health Organisation defined an endocrine disruptor as “an exogenous substance or mixture that alters functions of the endocrine system and consequently causes adverse health effects in an intact organism, or its progeny or (sub) populations” (World Health Organization, 2017). ED’s can work via a number of mechanisms. One way is through mimicking the natural hormones within the body closely enough that they can exert that hormones activity, having the same effect on the body. On the other hand, ED’s can block the activity of the hormone which interferes with the communication. Figure 3 summarises ways in which endocrine disruptors can work (National Institute of Environmental Health Services, 2017). One of the main challenges within the field of endocrinology and the study of ED’s is that the substances that act as ED’s are very diverse with many not sharing any structural similarity other than usually being small molecular mass compounds (Diamanti-Kandarakis et al., 2009). Figure 3. A diagram showing ways in which endocrine disruptors can operate Health effects of ED’s Throughout the decades there has been evidence accumulating that exposure to environmental chemicals and pollutants have had a negative impact on humans and wildlife because of their interaction with the endocrine system (Kavlock et al., 1996). There are factors with endocrine disruption that make their effects difficult to monitor. These include the age of exposure as the consequences of the exposure may differ between a foetus, child or an adult. The phrase “the foetal basis of an adult disease” has been associated with endocrine disruption for this reason. The maternal environment, the egg and the external environment all interact with the individual’s genes to determine the probability of that individual to develop a disease in their later life. The latency from exposure can mean there is a lag time between the time of exposure and the effects of the ED. A person may encounter exposure of an endocrine disrupting chemical however the consequences many not be immediately apparent and could take years for the effects to become apparent. There can be an additive or synergistic effects of ED’s as it is rare that one single EDC can cause major effects. These effects can be additive or synergistic. Finally, ED’s may affect the children of the exposed subject causing transgenerational epigenetic effects. More recent studies show that the effects may be transferred through the modification of gene expression for example DNA methylation and histone acetylation (Diamanti-Kandarakis et al., 2009).  What the literature saysUV filters are used in many products such as cosmetics, adhesives, plastics and other industrial substances to block or absorb UV rays and reduce UV radiation. In cosmetics and sunscreens UV filters are extremely beneficial in terms of protection against UV rays as they will either reflect, scatter or absorb UV rays as opposed to the skin absorbing them. UV filters can absorb or reflect UV A and UV B light with specific wavelengths between 320nm – 400 nm and 290nm and 320 nm (Wang et al., 2016). Without the use of UV filters, the skin is exposed to UV rays which can damage DNA in skin cells, cause mutation and lead to skin cancer. The US Food And Drug Administration (USDA) and the EU Scientific Committee on consumer products has permitted the use of 29 UV filters in cosmetics (Data.europa.eu, 2017)with maximum concentrations for individual UV filters of 10% except for Drometrizole Trisiloxane with 15% (Jiménez-Díaz et al., 2013). Research suggests that UV filters have a maximum skin penetration up to 5% with the total amount of compound absorbed from one application being up to 200 mg (Ruszkiewicz et al., 2017). Table 2 shows the UV filters that are permitted in personal care products (Sfda.gov.sa, 2017). Various studies have however shown that UV filters can be bioaccumulated within organisms because of their stability, resistance and lipophilicity which can induce toxicities within organisms and act as ED’s.  A study involving thirty-two male and female Caucasians found that after using sunscreen for a week the UV filters benzophenone – 3, 4-methylbenzylidene camphor and octyl-methoxycinnamate were all absorbed into the skin and secreted in the urine demonstrating the skin penetration abilities of UV filters (Janjua 

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