diff --git a/code/__HELPERS/lists.dm b/code/__HELPERS/lists.dm
index cfb6d9d2108..7076565f541 100644
--- a/code/__HELPERS/lists.dm
+++ b/code/__HELPERS/lists.dm
@@ -313,4 +313,11 @@ proc/listclearnulls(list/list)
 		if(index == i)
 			return key
 		i++
-	return null
\ No newline at end of file
+	return null
+
+/proc/count_by_type(var/list/L, type)
+	var/i = 0
+	for(var/T in L)
+		if(istype(T, type))
+			i++
+	return i
\ No newline at end of file
diff --git a/code/modules/clothing/masks/breath.dm b/code/modules/clothing/masks/breath.dm
index 08e60eadafa..2279d06aeaf 100644
--- a/code/modules/clothing/masks/breath.dm
+++ b/code/modules/clothing/masks/breath.dm
@@ -12,4 +12,5 @@
 	desc = "A close-fitting sterile mask that can be connected to an air supply."
 	name = "medical mask"
 	icon_state = "medical"
-	item_state = "medical"
\ No newline at end of file
+	item_state = "medical"
+	permeability_coefficient = 0.01
\ No newline at end of file
diff --git a/code/modules/clothing/masks/miscellaneous.dm b/code/modules/clothing/masks/miscellaneous.dm
index ad99984d7c1..d0d3ebe8e82 100644
--- a/code/modules/clothing/masks/miscellaneous.dm
+++ b/code/modules/clothing/masks/miscellaneous.dm
@@ -24,7 +24,7 @@
 	w_class = 1
 	flags = FPRINT|TABLEPASS|MASKCOVERSMOUTH
 	gas_transfer_coefficient = 0.90
-	permeability_coefficient = 0.05
+	permeability_coefficient = 0.01
 	armor = list(melee = 0, bullet = 0, laser = 0,energy = 0, bomb = 0, bio = 25, rad = 0)
 
 /obj/item/clothing/mask/fakemoustache
diff --git a/code/modules/clothing/shoes/colour.dm b/code/modules/clothing/shoes/colour.dm
index e9930cda953..4edc78a46ec 100644
--- a/code/modules/clothing/shoes/colour.dm
+++ b/code/modules/clothing/shoes/colour.dm
@@ -65,7 +65,7 @@
 /obj/item/clothing/shoes/white
 	name = "white shoes"
 	icon_state = "white"
-	permeability_coefficient = 0.25
+	permeability_coefficient = 0.01
 	color = "white"
 
 /obj/item/clothing/shoes/rainbow
diff --git a/code/modules/mob/mob_cleanup.dm b/code/modules/mob/mob_cleanup.dm
index 6b032a9c077..ab11546364d 100644
--- a/code/modules/mob/mob_cleanup.dm
+++ b/code/modules/mob/mob_cleanup.dm
@@ -22,10 +22,7 @@ Put (mob/proc)s here that are in dire need of a code cleanup.
 		if(A.GetDiseaseID() in resistances)
 			//world << "It resisted us!"
 			return
-		var/count = 0
-		for(var/datum/disease/advance/AD in viruses)
-			count++
-		if(count >= 3)
+		if(count_by_type(viruses, /datum/disease/advance) >= 3)
 			return
 
 	else
@@ -118,41 +115,33 @@ Put (mob/proc)s here that are in dire need of a code cleanup.
 			if(1)
 				if(isobj(H.head) && !istype(H.head, /obj/item/weapon/paper))
 					Cl = H.head
-					passed = prob(Cl.permeability_coefficient*100*virus.permeability_mod)
-//					world << "Head pass [passed]"
+					passed = prob((Cl.permeability_coefficient*100) - 1)
 				if(passed && isobj(H.wear_mask))
 					Cl = H.wear_mask
-					passed = prob(Cl.permeability_coefficient*100*virus.permeability_mod)
-//					world << "Mask pass [passed]"
+					passed = prob((Cl.permeability_coefficient*100) - 1)
 			if(2)//arms and legs included
 				if(isobj(H.wear_suit))
 					Cl = H.wear_suit
-					passed = prob(Cl.permeability_coefficient*100*virus.permeability_mod)
-//					world << "Suit pass [passed]"
+					passed = prob((Cl.permeability_coefficient*100) - 1)
 				if(passed && isobj(slot_w_uniform))
 					Cl = slot_w_uniform
-					passed = prob(Cl.permeability_coefficient*100*virus.permeability_mod)
-//					world << "Uniform pass [passed]"
+					passed = prob((Cl.permeability_coefficient*100) - 1)
 			if(3)
 				if(isobj(H.wear_suit) && H.wear_suit.body_parts_covered&HANDS)
 					Cl = H.wear_suit
-					passed = prob(Cl.permeability_coefficient*100*virus.permeability_mod)
-//					world << "Suit pass [passed]"
+					passed = prob((Cl.permeability_coefficient*100) - 1)
 
 				if(passed && isobj(H.gloves))
 					Cl = H.gloves
-					passed = prob(Cl.permeability_coefficient*100*virus.permeability_mod)
-//					world << "Gloves pass [passed]"
+					passed = prob((Cl.permeability_coefficient*100) - 1)
 			if(4)
 				if(isobj(H.wear_suit) && H.wear_suit.body_parts_covered&FEET)
 					Cl = H.wear_suit
-					passed = prob(Cl.permeability_coefficient*100*virus.permeability_mod)
-//					world << "Suit pass [passed]"
+					passed = prob((Cl.permeability_coefficient*100) - 1)
 
 				if(passed && isobj(H.shoes))
 					Cl = H.shoes
-					passed = prob(Cl.permeability_coefficient*100*virus.permeability_mod)
-//					world << "Shoes pass [passed]"
+					passed = prob((Cl.permeability_coefficient*100) - 1)
 			else
 				src << "Something strange's going on, something's wrong."
 
@@ -169,11 +158,11 @@ Put (mob/proc)s here that are in dire need of a code cleanup.
 			if(1)
 				if(M.wear_mask && isobj(M.wear_mask))
 					Cl = M.wear_mask
-					passed = prob(Cl.permeability_coefficient*100+virus.permeability_mod)
+					passed = prob((Cl.permeability_coefficient*100) - 1)
 					//world << "Mask pass [passed]"
 
-	if(passed && spread_type == AIRBORNE && internals)
-		passed = (prob(50*virus.permeability_mod))
+	if(!passed && spread_type == AIRBORNE && !internals)
+		passed = (prob((50*virus.permeability_mod) - 1))
 
 	if(passed)
 		//world << "Infection in the mob [src]. YAY"