It is important to know some of the basic characteristics of the planet Mangal i.e. Mars prior to discuss Manglik Dosha. Mangal is red hot planet and known as commander among all the planets. Being a planet of tamsik and fiery nature, it signifies battle, energy, strength (physical) and power, Mars has command over blood and muscles of our body. Mars is also karaka (significator) for the younger brother, sexual strength and passion. As it is very aggressive and powerful it represents courage and confidence of the native.

Natives with stronger Mars are found to be more dynamic, energetic, courageous, and stronger that’s why they are found more in Army, Police or where muscle power is prominently needed. Out of 12 rasis, Mars is the Lord of Arise (Mesh) and Scorpio (Vrishchik), Fighter Mars gets exalted i.e. become very strong in enemy’s sign (Capricorn – Makar rasi, lordship of rigid Saturn) and becomes debilitated (very weak) in sweet and cool sign Cancer (Karka rasi, lordship of sweet Moon). Only A great fighter can have such kind of nature. Main deity of Mangal is Lord Hanuman ji, Mother Durga and Mother Baglamukhi. Ruling direction of Mangal is south. Mangal is regarded as son of mother earth that’s why its another name is Bhumi Putra.


What is Mangal Dosha

It is said that if Mangal i.e.Mars is located in houses 2nd, 12th, 4th, 7th, and 8th, house in the horoscope of a girl it will lead to the death of husband or if it is in the horoscope of a male it will kill his wife. The basis for this is following Sanskrit Sloka:
 
Dhanvayaye or patale jamitre or ashtame kuja:
 Strinma bhartri vinashach bharatarunam strishanam
 
Which means if mars is in the 2nd, 12th, 4th, 7th, and 8th, houses in the horoscope of a female, the death of the husband will occur.
Similarly placed in husband’s horoscope leads to death of wife.” some scholars are of the opinion that 1st house should also be included because from here Mars aspects the 7th house.
    
These houses have to be judged from Lagna only. However, some scholars count from Moon also.

Why Only Selected Houses:

Mars in the 1st house:  It makes a person very strong, dynamic, energetic, angry, passionate and aggressive. From this house it directly aspects 4th house of mental peace and 8th house of longevity of marriage (as it is 2nd from 7th, the house of marriage) and 7th house , which is the house of marriage so his/her nature will definitely be very dominating towards spouse, This is the first type of Manglik dosha.


Mars in the 2nd house. The 2nd house represents kutumba or family. From here it also aspects the eight and hence it is bad for longevity of marriage.

Mars in 4th house: Mangal is energetic planet, natives spend most of his/her energies in whichever house it is present. If it is in 4th house native spends most of his/her energies in home only, family atmosphere gets tensed and annoying, small conflicts and arguments would always be there, from here too Mars directly aspects 4th house , i.e. 7th house again his domination towards spouse would suffer married life.

Mars in 7th house: The 7th house deals in marriage, relationships and physical relationship, anger, aggressiveness. Mars forces native to spend his energy in passion or anger in married life. It also gives fear or chances of accidents to the spouse.

Phaladeepika says, person wanders on road and loses his wife if Mars is in the 7th house and
according to the Saravalli the subject’s wife dies, native will be unhappy and leads a sinful life.

Mars in the 8th house: Eight represents longevity of husband or wife. It is also a house of saubhagya and length of married life. Mars in the eight houses has been universally condemned in the astrological literature. It is supposed to give following results-
1)    it is said to effect the longevity of the person or the spouse
2)    Accidents, injuries to the person may happen.
3)    One gets hindrances in all walks of life. It is said that well placed planets in Kendra’s and Trikonas are not able to give full effect because of the placement of the Mars in the eighth.

Mars in the 12th house: 12th house of chart deals in losses, secret enemies, secret desires and pleasure of bed. Here native may became very introvert, he/she may not be able to tell his/her desires, he may fulfill his/her desires secretly or he may become violent while enjoying pleasure. From this house too, Mars directly aspects the 7th house.

Therefore the placements of Mars in these houses are detrimental to the spouse and hence are known as Mangal dosha. This condition is believed to be devastating for marriage, causing discomfort and tension in relationship, leading to separation and divorce. It is believed to cause untimely death of one spouse.  Some believe that one Manglik should only marry another Manglik, the idea being that two negatives cancel each other out, creating a positive. People also believe in "Poojas" that can be performed to allow Manglik and Non-Manglik to marry each other. There are also beliefs that astrological remedies (Upayas) can be used to resolve this Mangal Dosha.

As there are 12 houses in a horoscope and Mars in 6 houses causes Mangal Dosha, it simply means that 50% of the people born haveMangal Dosha of some level. If you count houses from both lagna and from Moon, 50% would increase up to 75%. Hence it goes without saying that this Mangal Dosha is not something which will ruin a person. The prevalent misconceptions are that, if a person has a malefic mars it will either ruin the marriage or will cause one's death or the death of the partner. Especially if a girl has Kuja or Mangal Dosha, called "Mangali", she is looked upon as a devil by the in-laws. This is not always true.

A proper and thoughtful consideration on Mangal Dosha can help avoid post-marital problems. Mars is a planet that represents fire. It causes a Mangal dosha in the chart because it tends to ignite the house in which it is placed and over which it has 100% aspect. Mars is a planet of valour and vigour and if occupies in the lagna, it makes the person brave and headstrong. Why should then these qualities work against a relationship? Mars alone would not decide the fate of the relationships. The placement of all the planets has to be studied as it modifies the impact of mars and gives a blended effect.

Cancellation of Mangal Dosha    
    
1. It is believed that if such a dosha is found in both the horoscopes of bride and bridegroom the dosha gets cancelled.
2. If one of them has Mars in lagan, the 2nd, 4th, 7th, 8th, or 12th, and the other Saturn, Rahu or ketu in any one of the above houses then too, the defect gets cancelled.
3.  It is also believed that this dosha does not operate after 28 years of life.
4. When Mars is in its own sign (Aries, Scorpio), exalted (Capricorn) or in the houses owned by PLANETS SUPPOSED to be its friends (Sun, Jupiter, Moon) Mangal dosha gets cancelled.
5. If Mars is in the 2nd house but in Gemini, Virgo sign then the Mangal dosha gets cancelled
6. If Mars is in 12th house but in Taurus, Libra then the Mangal dosha gets cancelled.
7. If Mars is in 7th house but in Cancer, Capricorn then the Mangal dosha gets cancelled.
8. If Mars is in 8th house but in Sagittarius, Pisces no dosha exists.
9. For Cancer and Leo ascendant Mars is a yoga karaka (a beneficial influence) wherever it may be no dosha exists at all.
10. For Aquarius ascendant Mars in the 4th/8th house then the Mangal dosha gets cancelled.
11. If benefic Jupiter or Venus is in ascendant, no dosha exists.
12. If Mars is in conjunction or aspected by Jupiter or Moon no dosha exists.
13. If Mars is in conjunction/aspected by Sun, Mercury, Saturn, Rahu then the Mangal dosha does not exists.

These and many more rules for cancellation should be studied carefully before stating the malefic effects of Mangal dosha. The matching of horoscopes and especially the extent of Mangal Dosha is the job of an experienced astrologer and must be done after carefully analyzing both the horoscopes.