Q. Is menstruation actually a taboo in vedic Dharma ? If not then why women aren't allowed in some temples ?
A. No menstruation isn't a taboo in vedic Dharma , infact we have temples where menstruation is celebrated. Kamakhya Devi also called bleeding goddess is worshipped (1/n)

At Kamakhya Devi temple . In month of June (Ashaad) Brahmaputra river turns red near temple

Q.Then why some temples don't allow menstruating women ?
A. Worshipped means Sadhna for union of Jeeva and Brahman or union of individual energy with universal cosmic energy (2/n)

A menstruating woman is called Rajasva stri , a state where Rajasva qualities are at its peak . She is going through a process of purification (shift from impurity of bodily fluid to purity of body system) hence both impure+pure (in physiological terms) (3/n)

During menstruation when a woman become purest ,she becomes vulnerable to different energies (positive and negative both) . Ancient temples are energy centre dealing with divine energies . Idols are installed there by Pran Pratiksha (adding life force ) (4/n)

Since worship is Sadhna ,process of union of individual energy ( as kundalini at base of spine) with cosmic energy (in sahasrara chakra at top of head) .so energies are needed to be elevated from base of spine to top of skull i.e, upward motion of energy (5/n)

But during menstruation a woman undergoes downward flow of energies , hence women are suggested not to visit those temples during menstruation , its all related to body physiology and cosmic energies . In early times women were given rest of 5 days too . So women aren't impure .

There are many temples where men aren't allowed during some specific period (article link at the end of thread ) (7/n)

Since we've used many source of information , we can't mention all of them but we're thankful . I hope this thread is useful and informative
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https://curlytales.com/womens-only-temples-in-india-where-men-are-not-allowed/