Introduction-Impurity versus filth: It was explained above a list of actions that cause an impure spirit to reside on the hands. In the Q&A there it was explained that it is permitted to learn Torah and recite blessings prior to washing off the impure spirit from one’s hands. Nevertheless there remains a prohibition to learn Torah and recite blessings with unclean [i.e. dirty] hands. Not all of the actions which bring an impure spirit dirty the hand. Likewise not all actions that dirty the hands bring an impure spirit.[2] The Halachic ramification between impurity and filth is that if an action only causes filth then although he must clean his hands prior to prayer or Torah learning he is not required to do so specifically with water. If it causes an impure spirit, but not filth, then although he must wash his hands with water, he may learn Torah beforehand. If the action causes both impure spirit and filth then he must wash his hands to remove the impure spirit and may not learn Torah until he cleans them. The list of actions that dirty the hand and hence prohibit Torah study and blessings will be discussed in this Halacha.

A. The law:[3]  

It is forbidden to learn Torah or recite blessings with dirty hands.

Thinking words of Torah:[4] It is permitted to think words of Torah prior to cleaning one’s hands that were dirtied due to the actions to be mentioned.

Q&A

May one answer Amen prior to cleaning the hands?[5]

This matter requires further analysis. [One may however quickly wipe his hands on his clothing and then answer Amen.]

If one heard thunder or saw lightning may he say the blessing prior to cleaning his hands?[6]

No.

What is one to do if he heard Kaddish or Kedusha prior to washing the hands?

He is to quickly wipe his hands on his clothing and then answer.

May one pray a personal prayer to Hashem with unclean hands?[7]

Yes. It is permitted to pray a personal prayer so long as one does not mention Hashem’s name.

B. List of actions:

The hands are considered dirty after performing any of the following actions. [This applies even if the hands do not visibly appear dirty.[8]]

1. Hands that touched the normally covered areas of the body.[9]
2. Hands that scratched ones head.[10] (However one who merely placed his hands on his head, or even rubbed his head such as to dry his hair, but did not actually scratch between the hairs, is not required to wash.[11])
3. One who touched ear wax.[12]
4. One who touched mucus from his nose. [13] [If however the mucus is dry one is not required to clean his hands unless he touched the inside of his nose.[14]]
5. One who slept naked[15] [or without being fully clothed[16], even during the day.[17]] [This however only applies if one slept a set sleep. If however one slept a temporary sleep then he may learn Torah and recite blessings even prior to cleaning the hands.[18] The same applies if during the day he slept a set sleep but was fully clothed.[19] Nevertheless it is necessary to eventually wash the hands in order to remove the impure spirit as explained in Halacha 4A.]
6. Learning Torah and reciting blessings after using the bathroom, prior to cleaning the hands:[20] If one used his hands to wipe himself, [or he touched a normally covered area while using the bathroom[21]] he is required to clean his hands prior to learning Torah or reciting blessings. If however he did not dirty his hands or touch any normally covered part of his body then he is not required to wash [or clean] his hands prior to learning or reciting a blessing. Nevertheless even in such a case it is proper to wash ones hands. 

One who used a cloth to touch any of the above areas:[22] One who touched any of the above areas with a cloth is not required to clean his hands.

Other bodily fluids:[23]

The rule is that all bodily fluids that are viewed as repulsive and dirty require the hands to be cleaned from them upon touching it, prior to learning Torah or reciting Hashem’s name. The following is a general list of fluids and their law:

• Blood: Plain blood does not need to be cleaned off the hands. However blood of an infected wound requires cleaning. A Rav who looks at a Maarah is required to clean his hands if the cloth was dirty in addition to the blood.
• Bandage: Touching a dirty bandage requires cleaning of the hands.
• Puss: Touching the puss of a wound or pimple requires the hands to be cleaned
• Tears: Touching tears do not require the hands to be cleaned.
• Mucus of the eyes: Touching mucus of the eye does not require the hands to be cleaned.[24]
• Saliva: Some[25] rule that touching saliva does not require the hands to be cleaned. Others[26] rule saliva is disgusting and hence requires the hands to be cleaned.
• Feces: Touching feces requires the hands to be cleaned.
• Urine: Touching urine requires the hands to be cleaned.

Must one clean his hands if he touched a potty?[27]

If the potty is clean one is not required to clean his hands prior to learning or prayer. If the potty is dirty one needs to clean the hands. This applies by potties of all materials.

Must one clean his hands if he touched a diaper or baby wipe?[28]

If the diaper or baby wipe is dirty he is to clean his hands. If it is clean he is not required to clean his hands. However some Poskim[29] rule one is to clean his hands even in such a case.

Must one clean his hands if he touched mud or other filth?[30]

Yes.

If one slept during the day with an undershirt that has a low neck line must he clean his hands prior to learning Torah or reciting blessings?[31]

Yes, as we assume he touched the area of his chest that is normally covered and contains sweat. This is in addition to the requirement to wash hands due to the impure spirit.