involved in adaptive behaviors, such as parental attachment in infants or partner choice in adults. "mothers can discriminate the odor of their own child, and infants recognize and prefer the body odor of their mother over that of another woman. this maternal odor appears to guide infants toward the breast and to have a calming effect." body odor is involved in the development of infant–mother attachment and is essential to a child's social and emotional development and evokes feelings of security. reassurance created by familiar parental body odors may contribute significantly to the attachment process. human body odors can also affect mate choice. fragrances are commonly used to raise sexual attractiveness and induce sexual arousal. researchers found that people choose perfume that interacts well with their body odor. body odor is a sensory cue critical for mate selection in humans because it is a signal of immunological health. women prefer men with major histocompatibility complex (mhc) genotypes and odor different from themselves especially during ovulation. different mhc alleles are favorable because different allele combinations would maximize disease protection and minimize recessive mutations in offspring. biologically females tend to select mates "who are most likely to secure offspring survival and thus increase the likelihood that her genetic contribution will be reproductively viable." studies have suggested that people might be using odor cues associated with the immune system to select mates. using a brain-imaging technique, swedish researchers have shown that gay and straight males' brains respond in different ways to two odors that may be involved in sexual arousal, and that the gay men respond in the same way as straight women, though it could not be determined whether this was cause or effect. the study was expanded to include lesbian women; the results were consistent with previous findings that lesbian women were not as responsive to male-identified odors, while their response to female cues was similar to that of straight males. according to the researchers, this research suggests a possible role for human pheromones in the biological basis of sexual orientation. an odor can cue recall of a distant memory. most memories that pertain to odor come from the first decade of life, compared to verbal and visual memories which usually come from the 10th to 30th years of life. odor-evoked memories are more emotional, associated with stronger feelings of being brought back in time, and have been thought of less often as compared to memories evoked by other cues. use in design the sense of smell is not overlooked as a way of marketing products. the deliberate and controlled application of scent is used by designers, scientists, artists, perfumers, architects, and chefs. some applications of scents in environments are in casinos, hotels, private clubs, and new automobiles. for example, "technicians at new york city’s sloan-kettering cancer center disperse vanilla-scented oil into the air to help patients cope with the claustrophobic effects of mri testing. scents are used at the chicago board of trade to lower the decibel level on the trading floor." if ingredients are listed on a product, the term "fragrance" can be used in a general sense. scent preferences effect of perfume on sexual attractiveness both men and women use perfume to boost their sexual attractiveness to members of the opposite, or same, sex. when people find that a particular perfume or aftershave is perceived positively, they may be hard-pressed to change it. olfactory communication is natural in humans. without perfume or aftershave, humans unconsciously detect people's natural scents: in the form of pheromones. pheromones are usually detected unconsciously, and it is believed that they have an important influence on human's social and sexual behaviour there are a number of hypotheses concerning why humans wear perfume or aftershave, and whether it amplifies or reduces their natural scents. in 2001, a study found that the major histocompatibility complex (mhc) (a polymorphic set of genes which is important for immune-function in humans) is correlated with the ingredients found in perfume. this suggests that humans do, in fact, choose perfumes that complement or enhance their natural scents (their pheromones). this evidence offers support for the hypothesis that perfume is chosen by individuals to advertise their physical health. research suggests that this advertisement of good health will, in fact, enhance females’ attractiveness to the opposite sex as health markers have been shown to do. while strong evidence has been found to support the hypothesis that wearing perfume enhances females’ attractiveness to males, little research has been done into the effect of fragrance on males’ attractiveness to females. considerably more research has covered the effect of males’ natural odor and females’ ratings of attractiveness. many studies found that odor predicted attractiveness when female raters were not on any form of contraceptive pill. for those who were, there was no relation between attractiveness and body odor. a person's odor can increase or decrease ratings of attractiveness because the olfactory receptors in the brain are directly linked with the limbic system, the part of the brain that is thought to be most involved with emotion. this link is important, because if an individual associates positive affect (elicited by pheromones), with a potential mate, their liking for, and attraction to, that potential mate will be increased. although not a typically evolutionary hypothesis, this hypothesis is one that acknowledges how humans have adapted their mating strategies to modern-day societal norms. major histocompatibility complex (mhc) and body odor preferences major histocompatibility complex (mhc) is a genotype found in vertebrates, including humans. mhc is thought to contribute to mate choice in animals and humans. in sexual selection, females opt for mates with an mhc which differs from their own, optimising genes for their offspring. the "heterozygote advantage" and "red queen" explanations for these findings fall under the "pathogen hypothesis". due to differences in mhc alleles' resistance to pathogens, a preference for mates with a dissimilar mhc composition has been argued to act as a mechanism to avoid infectious diseases. according to the heterozygotes-advantage hypothesis, diversity within the mhc genotype is beneficial for the immune system due to a greater range of antigens available to the host. therefore, the hypothesis proposes that mhc heterozygotes will be superior to mhc homozygotes in fighting off pathogens. experimental research has shown mixed findings for this idea. the "red queen" or "rare-allele" hypothesis suggests that diversity in the mhc gene provides a moving target for pathogens, making it more difficult for them to adapt to mhc genotypes in the host. another hypothesis suggests that preferences for mhc-dissimilar mates could serve to avoid inbreeding. body odor can provide mhc information. although less is known about how odor is influenced by mhc genes, possible explanations have been that microbial flora or volatile acids are affected by the gene, which can be detected in body odor. female mice and humans have both shown odor preferences for males with mhc-dissimilarity. research has shown that women prefer the scent of men with dissimilar mhc genes. in a study, women rated the scent of t-shirts, worn over two nights by men, as more pleasant when smelling those of mhc-dissimilar men. it has also been found that women were reminded more of current or prior partners when smelling odors from men whose mhc was dissimilar to their own. a study of married couples found that mhc haplotypes differed between spouses more than chance would dictate. taking oral contraceptives has been found to reverse the mhc-dissimilarity odor preference. women's scent preferences and the menstrual cycle women's preferences for body odor change with their menstrual cycles. the ovulatory-shift hypothesis argues that women experience elevated immediate sexual attraction, relative to low-fertile days of the cycle, to men with characteristics that reflect good genetic quality. body odor may provide significant cues about a potential sexual partner's genetic quality, reproductive status, and health, with a woman's preferences for particular body odors becoming heightened during her most fertile days. as certain body odors can reflect good genetic quality, woman are more likely to prefer these scents when they are fertile, as this is when they are most likely to produce offspring with any potential mates, with conception-risk being related to a preference for the scent of male symmetry. men also prefer the scent of women at their fertile cycle points. there are several scents that reflect good genetic quality that females prefer during the most fertile phase of their cycles. women prefer the scent of symmetrical men more during the fertile phases of their menstrual cycle than during their infertile phases, with estrogen positively predicting women's preferences for the scent of symmetry. women's preferences for masculine faces is greatest when their fertility is at its highest, and so is the preference for attractive faces. other scents found to be preferred by women in the most fertile phase of their cycle are the scent for developmental stability, and the scent for dominance. if women are taking a contraceptive pill the changes in mate scent preferences over the menstrual cycle are not expressed. if odor plays a role in human mate choice then the contraceptive pill could disrupt disassortative mate preferences. those taking a contraceptive pill show no significant preference for the scent of either symmetrical or asymmetrical men, whereas normally cycling women prefer the scent of shirts worn by symmetrical men. males' preferences for women's scent may also change if the woman is taking oral contraceptives. when women take a contraceptive pill, this has been found to demolish the cycle attractiveness of odors that men find attractive in normally ovulating women. therefore, a contraceptive pill affects both women's preferences for scent and also affects their own scents, making their scent less attractive to males than the scent of normally cycling women.