Why do unmarried women worship Shiva on 16 Mondays in Chaturmas starting from the month of Shravan?

Shravan is the first month of Chaturmas, which forms the first four months of Dakshinayana. 

During Dakshinayana the days are shorter and the nights are longer, there are more levels of melatonin compared to serotonin in the body and there are tendencies for spontaneous negative thoughts in the mind. Kama or desire is the first negative thought, which gets exaggerated in this period.

Shravan is the month linked to a disturbed state of mind. There is a famous song which describe the mental status of a mind in the shravan, i.e. “Sawan Ka Mahina Pawan Kare Shor”, which means that just as in the month of Shravan the air in atmosphere is disturbed and violent so is our mind.  

The answer lies in controlling our desires in the month of Shravan. Unmarried and married fertile women do it by following the ritual of Shiva Vrata on  Mondays ( the first day of the week) and man do it by participating in Kanwar yatra from Ganga river to the respective Shiva Linga Mandir.

Unmarried women and married women observing Monday fast indicates observing a sexual and non-sexual desire fast.  

You cannot enter in a Shiva temple with your sexual desires.  Therefore, you keep your Nandi (Bull sexual desire) outside the temple.

Some scholars co-relate Shiva Lingam as your internal Lingam, which you try to control by pouring milk onto it. A continuous flow of milk represents continuous flow of positive thoughts.  By controlling the sexual desires for 16 consecutive weeks, the sexual energy can be converted into a more forceful spiritual energy.

Both sexual and non-sexual desires are equally common in unmarried and married man who to control their desires need to make more efforts and thereby need to devote time.  

In the month of Shravan in the “Kanwar yatra” people walk for days together and reach Ganga destination and bring Gangajal to be poured over the Shiva Lingam.  This again indicates continuous mental and physical efforts on the part of the person to earn positive thoughts (Ganga) and with that to pacify the sexual and non-sexual desires (Shiva Lingam). 

This way one converts again sexual energy and the non-sexual desires into spiritual energy.  The observance of fast apart from Shiva Lingam worship helps in controlling five sensual senses in the mind and the body.