Vaginal mucus is a natural substance occurring within the vagina

Vagina

The vagina is a fibromuscular tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the...

, particularly the cervix

Cervix

The cervix is the lower, narrow portion of the uterus where it joins with the top end of the vagina. It is cylindrical or conical in shape and protrudes through the upper anterior vaginal wall...

, that maintains a certain level of moisture at all times.

The volume, color, and consistency of vaginal mucus changes according to the period of the menstrual cycle

Menstrual cycle

The menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purpose of sexual reproduction. This article focuses on the human menstrual cycle....

. Both the chemical make-up and the physical consistency (viscosity

Viscosity

Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

) change during this time. A slippery, clear, egg white

Egg white

Egg white is the common name for the clear liquid contained within an egg. In chickens it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. It forms around either fertilized or unfertilized egg yolks...

-like consistency usually indicates that the woman is ovulating. Relative dryness usually indicates an infertile point in the menstrual cycle.

Excessive or oddly coloured mucus may indicate various infection

Infection

An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

s of the vagina or pregnancy

Pregnancy

Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...

.

As a sexual response

During sexual stimulation the blood vessel

Blood vessel

The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...

s fill inducing vasocongestion

Vasocongestion

Vasocongestion is the swelling of bodily tissues caused by increased vascular blood flow and a localized increase in blood pressure.Typical causes of vasocongestion in humans includes menstruation, sexual arousal, REM sleep, strong emotions, and illnesses and allergic reactions.-Illnesses:Menstrual...

. As a result, more fluids (largely sweat

SWEAT

SWEAT is an OLN/TSN show hosted by Julie Zwillich that aired in 2003-2004.Each of the 13 half-hour episodes of SWEAT features a different outdoor sport: kayaking, mountain biking, ice hockey, beach volleyball, soccer, windsurfing, rowing, Ultimate, triathlon, wakeboarding, snowboarding, telemark...

) are introduced to the genitals creating a higher level of moisture. This makes penetration of the vagina easier as it serves as natural vaginal lubrication

Vaginal lubrication

Vaginal lubrication is a lubricating fluid that is naturally produced in a woman's vagina. Vaginal lubrication or moistness is present at all times, but production increases significantly during a woman's sexual arousal in anticipation of sexual intercourse...

.