corneum and is an indicator of hydration and therefore of barrier function. TEWL varies with the number of cell layers in the epidermis, which in turn varies at different body sites. This number is lowest in the genital area [7], and it has been shown that water diffuses faster across the stratum corneum of the labium majus than the forearm [8,9], therefore increasing hydration. The occlusive environment may also play a part in this.
The coefficient of friction is higher on the vulva [9], making it more prone to mechanical damage. Friction can also be affected by occlusion, obesity, immobility, and use of sanitary wear. The vulva is less susceptible to irritants than forearm skin [10]. However, urinary ammonia levels will increase the pH and activate faecal enzymes, which will contribute to irritant features in patients with urinary incontinence [11].
The vulva is more permeable to hydrocortisone than the forearm [12], but this does not fall after the menopause as it does on the forearm. The difference in permeability and hydration will influence the effect and absorption of topically applied preparations [12,13], but it also has a practical application in cases of suspected contact irritancy and allergy. Routine patch testing may not be sufficient [14], and additional tests may be needed to allow for the effects of friction and epidermal morphology [15]. These physiological changes mainly studied in Caucasian women have also been confirmed in Asians [16].
Immune responsiveness
The skin is an important site for antigen presentation, and intact immune surveillance is an important defence against infection. The immune response in the genital tract has a unique task as it has to balance protection from infection against tolerance to sperm, the embryo, and foetus. The innate and adaptive immune systems are influenced by hormonal changes, so in the secretory stage of the menstrual cycle, infection is a greater risk as the immune response reduces to prepare for a potential pregnancy [17].
Langerhans cells play a vital role in the skin immune system, and the vulva has the highest density and the vagina the lowest in the female genital tract [18]. This does not vary with the menstrual cycle [19], but cell‐mediated immunity reduces after menopause.
Together with vaginal microbiota, the cervical mucus is an important component of the genital immune system. It contains antibodies, in particular secretory immunoglobulin A (IgA). This locally produced antibody is bactericidal in the presence of lysozyme and complement, and can agglutinate bacteria and present them for phagocytosis. It can also reduce the adhesion of the infective agent to the mucosa.
Protection against viral infection also requires an effective cytolytic T‐lymphocyte response. Patients who are immunosuppressed secondary to primary immune deficiency or medication have a significant risk of viral infection such as human papillomavirus (HPV) and its associated oncogenic disease [20]. It has also been shown that oral contraception can reduce immune responses to infections such as HIV [21].
Large numbers of spermatozoa enter the female reproductive tract during coitus, and these are destroyed by a coital immune response which is limited by the immunosuppressive function of seminal fluid to the immediate postcoital period [22]. This ensures that the embryo, which expresses paternal alloantigens, is not subject to immune attack during implantation. Seminal fluid can also induce inflammatory cytokines after intercourse [23]. The changes in immunity throughout pregnancy are much more complex [24].
Changes through life
These are summarised in Table 3.1.
Neonate
At birth the vulva is still under the influence of maternal hormones that cross the placenta and persist for about 4 weeks. The vagina will be lined with a stratified squamous epithelium rich in glycogen as a direct effect of maternal oestrogen, and lactobacilli will be part of the normal flora. There will often be an obvious vaginal discharge, which can be bloodstained as the result of the endometrium breaking down as oestrogen levels begin to fall.
Childhood
The labia minora are relatively prominent in childhood and as the hymen is thickened the vaginal orifice is difficult to see. The vestibule and introitus is normally bright red, and this often gives rise to the mistaken suspicion of abnormality. Due to reduced oestrogen levels, adhesions of the labia minora can be seen. These can mimic disorders of sexual differentiation and are sometimes mistaken for pre‐pubertal lichen sclerosus. A line of demarcation between the clitoral hood and the labia minora under the clitoris is seen with adhesions (see Chapter 51). Milia are sometimes seen on the labia majora in childhood.
Table 3.1 Normal changes in the vulva through life
| Labia majora | Labia minora | Vagina | Other | |
|---|---|---|---|---|
| Neonate | Fat is increased Milia (blocked eccrine ducts) may appear | Prominent | Lined by stratified epithelium, rich in glycogen Lactobacilli present | May be white or slightly blood‐ stained discharge |
| Childhood | Fat reduces | May form adhesions | Lack of glycogenation makes vagina more alkaline | |
| Puberty | Fat increases and also in the mons, which becomes more prominent Pubic hair appears | Become more covered by labia majora Increased pigmentation More rugose | Epithelium thickens Increased glycogenation of cells Lengthens Cervix glands active | Clitoris enlarges Urethral orifice more prominent Hymenal ring enlarges Bartholin’s glands become active |
| Reproductive years | May be increased parakeratosis mid‐cycle | pH increases during menses | ||
| Pregnancy | Increased blood flow giving a blue/purple appearance Varicose veins may appear Connective tissue relaxes Pigmentation | Look redder Rims may be more pigmented | Muscle fibres increase Thickening of vaginal mucosa and increased glycogen | Linea nigra Increased pigmentation Increased candida |
| Menopause | Loss of subcutaneous fat Reduced hair density and colour | Fordyce spots reduce in number and size | Reduced epithelial thickness Raised pH Pale Cervical and vaginal secretions reduce |
Before puberty, there is little glycogen in the vaginal epithelium, which therefore restricts the action of lactobacilli and the consequent acidification of the vaginal environment. The resultant relative alkalinity of the vaginal secretions increases susceptibility to vulvovaginitis and urinary tract infections.
Puberty
Puberty is related to gonadal maturation and the sex hormones that they start to produce. The physical changes associated with puberty are breast development, appearance of axillary and pubic hair, and the onset of the menses. Puberty is also accompanied by an increased growth rate. The timing of puberty