First of all, we’d like to make it clear that Ghusl (bathing the whole body) is obligatory in certain situations that a Muslim should know to be pure and eligible for Salah (ritual Prayer) and Tawaf (circumambulation) of the Ka`bah during Hajj and `Umrah.

Contact between the genitals is among things that require ghusl whether or not there is ejaculation. The Prophet (peace and blessings be upon him) said: “If one part enters the other part (in another report: if one part touches the other part), then ghusl becomes obligatory.” (Reported by Ahmad and Muslim) Touching” here refers to the entry of the tip of the penis into the vagina, not mere touching.

But when woman should perform ghusl after intimacy with her husband?

Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states that: “In case of seminal ejaculation one must perform ghusl (a complete bathing). This must be done whether ejaculation occurs while awake or asleep, or following sexual intercourse, masturbation, contemplation of sexual activity, or foreplay.
But, I must rush to add that seminal ejaculation is different from the usual wetness a man or woman experiences during foreplay or excitement. The latter, if not accompanied by intense feeling of pleasure (orgasm) is called madhy or prostatic fluid. In the case of madhy, one is not obliged to perform ghusl. He or she needs only to wash the genitals and make wudu’ (ablution).
If a woman experiences wetness while being excited or during foreplay, she is required to wash her private parts and perform wudu’; there is no need for ghusl unless it is accompanied by intense pleasure (orgasm).”