Tongue color ( shé sè) has been used to diagnose abnormal body conditions for thousands of years in traditional Chinese Medicine ( zhōng yī). However, it is not clear whether tongue color alters with physiological changes within a normal menstrual cycle ( yuè jīng zhōu qī). This study investigated difference in tongue color between the follicular phase and luteal phase in eumenorrheic women. Tongue surface photographs were taken in the follicular phase and the luteal phase of thirty-two volunteers with biphasic basal body temperature. Color values on five areas of the tongue surface were examined and comparisons of color values were made between the two phases according to the red-green-blue (RGB), hue-saturation-brightness (HSB), luminance-a-b (Lab), and cyan-magenta-yellow-black (CMYK) models. Based on the RGB model, the values of green and blue in the tip area were larger in the follicular phase than both in the luteal phase. The values of magenta and yellow based in the CMYK model were smaller in the tip area in the follicular phase than that in the luteal phase. The saturation in the tip area was smaller in the follicular phase than that in the luteal phase. Based on the Lab model, b value in the middle area was smaller in the follicular phase than that in the luteal phase. The data revealed that tongue color varied within a eumenorrheic menstrual cycle, suggesting that tongue color differences between the follicular and luteal phases need to be considered while practicing tongue diagnosis ( shé zhěn) or performing clinical studies among childbearing women.
Keywords: B (in HSB), brightness; B (in RGB), blue; BBT, basal body temperature; C, cyan; CMYK model; CMYK, cyan–magenta–yellow–black; E2, estradiol; G, green; H, hue; HSB model; HSB, hue–saturation–brightness; K, black; L, luminance; Lab model; Lab, luminance-a-b; M, magenta; Menstrual cycle; R, red; RGB model; RGB, red–green–blue; S, saturation; TCM, traditional Chinese Medicine; Tongue inspection; Y, yellow.