Brief Answer:
Mostly allergic, personal care/ expert advise would help.

Detailed Answer:
Hi XXXXX,
Thanks for the query under Health care magic platform.
I have read your query & understand your concern.

Itching on chest can be due to multiple causes.
They are-
-Allergy/Infection/ infestations / common skin problems like exema, psoriasis, contact dermatitis
* Itching caused by any of the above causes leads to neurodermatitis( it is a condition when scratching itself makes the skin more itchier,.. thus the itch- scratch cycle goes on to be intolerable). Similarly the numbness in left breast follows severe itching ( which injures tiny nerve fibers supplying breast skin ). It will disappear after few days.
In my view, your problem is due to allergy/ drying of skin.
* Allergy- It can be local allergy to things like Cosmetics (Soap,moisturizer, talcum power) / clothing material in use/ allergy to sweat.
*Dry skin caused by old age/ diabetes/ thyroid problems can also cause such an itch.

* In this scenario , I would suggest for primary consultation of your family doctor . He will examine you, get you investigated may send you to Allergy specialist/ endocrinologist for further evaluation & needful specific treatment as per need.
*Self care- Ttry to identify cause of allergy by observing any recent change in cosmetic use/ habit of having more sweat,/ food allergens/ getting allergic bronchitis after exposure to dust, fumes, specific food.
You may apply Steroid ointment with a tolerated skin moisturizer to alleviate too much of an itch./ A pill of tab. Cetrizine in the bedtimewill help.
- Use only cotton loose fitting clothes.

An expert's advise along with your own observations & tests would help to identify & manage the offending itching you are suffering from.
I hope the answer was both informative as well as useful to you. Any follow up query is welcome.
Thanks.

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